Fixing a Mystery Z80 Computer from the 1970s

I've had this Memodyne M-80 'mystery machine' for a number of years now but finally got tired of looking at it and decided to see if I could get it to actually do something. There's a Z80, ROM, RAM and serial I/O, not to mention storage.. gotta be a computer, right?
Link to the Memodyne M80 ROM dumps for those curious: drive.google.c...
Link to a brochure about similar machines I found: bitsavers.org/...
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[@TechTimeTraveller]

I've edited the video description to include the ROM dump I made, as well as a brochure someone found advertising similar Memodyne systems. I'd love to hear your thoughts on this machine and how we might test it further, or maybe even modify it into a standalone computer. While it clearly was aimed at people looking to record data in tricky places, I do think it qualifies as a general purpose computer, Memodyne clearly advertised that capability. Life goal: Play Zork off a tape. :) Also - apologies about the lower quality video - the camera somehow reverted to 1080p so my zoom ins didn't work as well as hoped. But there wasn't really anything intelligible showing up on the laptop screen anyway.

[@phill6859]

You can't run zork off tape as it constantly accesses disk. You will need more ram and some kind of fast random access storage. Then you might as well port CP/M to it.

[@TechTimeTraveller]

@phill6859 Oh yeah I'm just being a goof. I imagine it wouldn't be impossible though to create a disk controller for an external disk drive.

[@snakezdewiggle6084]

ISA 👉 USB is a thing.!

[@jnharton]

@@phill6859You could probably modify Zork to work from a tape drive, even if that's a crappy cassette deck. Having more than a couple K of ram would make things a lot easier. That said, it might really slow down your gameplay unless you can "cache" important parts of the game/z-machine interpreter. ----- Also, Zork I was released for a lot of different systems and did have at least one release on cassette tape (the one for C64).

[@jnharton]

@@TechTimeTraveller Creating a disk controller could be quite bit of work depending on what kind of drive you ended up using. I'd imagine that something using a flash chip/SD card for the media would be more trivial than a real 5 1/4" or 3.5" floppy disk drive.

[@UsagiElectric]

I absolutely adore this little box! I think other have mentioned it, but it sure looks like you're not quite there with baud rate settings yet. 7E1 is a more common setting, but also, I'm willing to bet the speed isn't quite right either. 1200 baud I think was a pretty common speed for tape decks, so the ROM could be indicating that. I would be willing to try 300, 1200, 2400, and 9600 for the terminal to see if you get any readable output out of the system. With that cool little laptop, swapping baud rates is pretty quick and easy. Or, you could put it in your luggage, fly down to Texas with it, and we'll get it going together! No guarantees I'll give it back after we finish filming with it though, haha.

[@TechTimeTraveller]

Always a pleasure to see you here! I did try off camera multiple different baud rates and settings including 7E1 and setting Hyperterminal to force it to 7 bit ASCII. The only reason I settled on 8N1 was the government document I mentioned finding. I believe in the section describing hookup they recommended those settings. And I agree I think the 1200 label on the EPROM is ambiguous.. it could be the baud rate it communicates with computer or could be to do with encoding tape deck. I don't know when I'll get to Texas but this thing is small enough maybe I can shoot it down to you for a more expert look one day. I did plan to do some followups to try and figure out the proper settings but have other stuff lined up.

[@jnharton]

Why not just pick a speed and play with the parity toggle and stop bits until you actually get something comprehensible? If nothing is seen, you could bump the speed and cycle all the other stuff again. Unless there's compression or an unusual encoding involved, I would think you'd get something coherent.

[@TechTimeTraveller]

@@jnharton I tried literally every combo off camera. It just wouldn't give me anything different unless I ramped up the speed and then I got nothing at allm

[@kc7klz]

@@TechTimeTraveller Typically when I'm attempting to communicate with an unknown serial device, I start with one setting (i.e. 8N1) and cycle through the baud rates. It sounds like you have done that. Did you notice any changes in the gibberish that was being sent? Is it sending ASCII text characters?? My thought is it was used to record data from an instrument of some sort like say an early version of a flight data recorder. Maybe it sent out pre-recorded digital signals like RTTY or some sort of data communication signal. It is a neat device. It would be fun to see if it you can actually get some usable signal off of it. I'm looking forward to seeing it in the future.

[@1RandomToaster]

I’m a simple woman, I see a video about something weird that might not even be a computer I click

[@Jayoldstuff1]

I have distant memories of one of these machines. Back in my collage days (late 90's) there was a very old CNC/milling machine in the engineering department, next to it was a console with a terminal on top and a computer exactly like that mounted underneath. Unfortunately I don't remember ever seeing it working. I believe it had been donated to the collage and don't think anyone at the collage actually knew how to operate it.

[@antoniosagamuccio7370]

Good catch. I've seen something very similar to these used to retrofit CNC equipment that had previously used punch-tape programs. IIRC chips had to be changed out to customize the unit for the particular I/O available on the different types of multi-axis lathes and different cards were used depending on whether digital and/or analog I/O was required. Have also seen "industrialized" tape based SCADA systems that look similar for remote location monitoring and transmitting of alarms with the addition of a modem.

[@thelegendarysupersquid7556]

This channel makes me want to get into vintage computing

[@TSteffi]

Just do it 😊

[@JohnGladden-camokub]

Don't know if you noticed this, but the color code of the card clips follows the resistor color code - (from right to left), black/brown/red/orange/yellow and the extra slots would accomodate green/blue/violet...

[@emuhill]

I've found some info on this over on the ClassicCMP website. Apparently it dates to around 1975. This deals with computer mainframes. Back then they were in the process of switching from the mechanical computer terminals to the CRT type. This device was designed to replace the old paper tape drives. It was hooked up inline between the terminal and the host mainframe. The connection to the mainframe could be a modem, a leased line, or a direct connection to the mainframe. My guess is that it was used to store and retrieve data by the user of the terminal using control sequence commands. If you want to get this working I would suggest finding an old computer with a serial port and run Linux on it. Hook the Linux computer up to one of the serial ports on the back of the M-80 and the laptop to the other serial port. Then play around with the control codes and see what it will do. Use the Linux computer to send data to the laptop and the laptop to send commands to the linux computer. See if you can record what the Linux computer is sending to the laptop and so on.

[@estebhann]

You are a true detective on arqueocomputing. Very interesting to see all the rational you follow, keeping it in the track, trying to reverse ingeneering how it works and how it does what it does. Wow, incredible. I take my hat off.

[@Metal_Maxine]

1:28 I'm sure all will be revealed, but having something with all the parts for a computer... it's giving me PET external floppy disk drive vibes.

[@BustaHymen]

My thought exactly! Isn't this just a mini variant of those old main frame "tape decks" which reads/writes data randomly instead of sequentially? Sure seems like it.

[@jnharton]

@@BustaHymen I take it you mean one of those crazy vacuum column high speed tape drives? So far as I know, there is no way to truly do random reads/writes to a tape drive or even a conventional spinning hard disk. At best you can minimize the time it takes to get the media moving and seek a particular spot on the media. Some form of validating you have the correct spot on the media is always necessary. For hard drives and floppy disks that would be hard/soft sectoring.

[@jnharton]

Yeah, this could be a 'smart' tape storage device, a single-purpose computer, or just some sort of weird standalone system. It can be really hard to tell what you've got just looking at one of these things without any documentation. I picked up a couple of cool early smart modems that achieve the "smart" via a Z80 cpu and support chips.

[@SockyNoob]

I sure do love mystery 70s machines. You never know what you're gonna get.

[@NiallWardrop]

A bit of information on RS232, obviously you figured it out for this machine but the 25 pin connector should be wired to the standard which was different depending on whether the equipment is Data Terminal Equipment (DTE) e.g. a computer or Data Communications Equipment (DCE) e.g. something like a modem. One uses a male connector and the other female, sorry, can't remember which is which, which implies that the two connectors on the back of this machine will be wired differently. The easiest way to identify DTE or DCE is to check whether pin 2 or 3 connects to one of the 1488 outputs, the other should connect to one of the 1489 inputs. Depending on whether pin 2 or 3 is Transmit, TXD, the 1488 output, the handshake pins will match. Which if any of the 2 pairs of handshake pins is implemented depends on the particular device.

[@NiallWardrop]

Looked it up. If pin 2 is TXD the connector is DTE, handshaking outputs are RTS on pin 4 and DTR on pin 20. RXD is pin 3, handshaking inputs are CTS on pin 5 and DSR on pin 6. Ground is pin 7. If it is DCE they are all swapped around, the idea being that a straight through male/female cable would be used. DTE should be the connector with the male pins, but this is not strictly adhered to.

[@bzuidgeest]

The first thing i noted was that you keep hyperterminal in hardware flow control mode. That requires very specific signaling and the necessary hardware flow control lines to be connected to work properly. The other options, software flow control and such are much more likely to show something or just work. I never had much hardware that did more than use rx and tx. I.e. software flow control. Second those boards are not complex, trace them out, create a simple schematic, can be done with pen and pencil. That would also help determine where in memory the serial board sits, which would help in decoding the ROM. Third verify the connections between the board, j1 and j2. Never assume it follows some standard, at the very least verify tx and Rx. Also modern scopes and such can often detect or guess the proper baudrate from the signaling if you have at least some activity. I don't want to sound negative, but you were really fumbling along, not very structural about it. You can have lucky guesses with undocumented hardware, but mostly your method seemed to be a crapshoot and you got unlucky. A more structural step by step approach will take more time, but will get you further in the end.

[@OscarSommerbo]

The flow control thing really bothered me. When testing, always turn off flow control to make sure nothing gets blocked or eaten. Next thing is on military/industrial of that era always assume 7n1 or 7e1, even just regular terminals used 7n1 because extended ASCII wasn't in wide use yet.

[@1RandomToaster]

In defense of the fumbling, that’s part of the learning process, especially when you don’t have a lot of tools. The structure thing though, that’s what turns fumbling into tinkering, and if you write that down that’s almost research 😅

[@brendn]

It’s an interesting video, and this comment is condescending.

[@bzuidgeest]

@@brendn ah, an fanboy. No criticisms allowed then?

[@henryokeeffe5835]

@@bzuidgeest If you are going to be so critical, at least be right. There's a difference between hardware flow control, software flow control and no flow control. Most hardware that just uses rx and tx has no flow control, not software flow control. Also, I think TTT is aware of his "fumbling along." Pointing it out does like that just make you sound condescending.

[@MotownBatman]

The Toughbook of its Time LOL I've seen those things get Run Over and still Tick. This is Awesome!

[@kardRatzinger]

I would put a logic analyser (or a scope) on the Tx pins of the SIO. This will tell you exactly what this computer is sending out (both in terms of format, i.e. baudrate etc, and actual content).

[@jnp-3r]

So that link to the brochure on similar machines appears to cover this machine too. At least the model numbers printed on the CPU card (402) Serial card (403) and overall system (M-80) line up. The only thing you're missing is the Model 411 Key Panel. That mystery red card is the Model 404 Phase Encoded Read Write Card, so you're right that's for encoding digital data into signals on cassette, though I'm not sure what exactly the "Phase encoded" signals are supposed to look like. I notice the block diagram on page 57 of the brochure shows the CPU card just behind the serial and cassette cards (the clips make a rainbow!) but I think you're also right that the last three slots are the same so that shouldn't matter. Also seems to be implied that these systems will be running software to suit the application so how it works, the baud rates, if it expects a serial terminal or commands in the data stream or any of that is up to the software in ROM. Your guess is as good as mine how it's set to work. The brochure mentions using it standalone in a lab with a terminal for control and running software, but it also mentions using it as a "slaved" system or a data logger. Haven't messed with industrial systems of this era, but a common thing for hobbyist dataloggers (like, for model rockets and such) is to just have the system listen to and record the serial data stream being sent in by the flight electronics, maybe with control codes to start / stop recording and to play things back. If you can't get response from serial that may be something to look into, and digging into ROM looks like the way to go there.

[@jnp-3r]

Also doing some more looking and it looks like Memodyne customized the firmware for each customer... Oof It also may be expecting a data stream *in* on the second port that it's recording. That may be why you don't see anything on the tape when trying to record.

[@jnharton]

Hobbyist data loggers these days would have an embedded computer in the form of a microcontroller, which might be solely for data logging or have a secondary/tertiary job.

[@jnp-3r]

@@jnharton Yeah, to clarify this was several years ago we were looking through the docs for that data logger, and it was a microcontroller system, just a fancy one with like, multiple real UARTS (no cheesy USI block), hardware SPI for an SD card, and a few megs of EEPROM tagged on the board for settings and secondary recording. This was before $5 micros and the explosion of Arduino, so a standalone product that let hobbyists focus on programming a single task (or just wiring up analog sensors if you got the version with A/D) and being able to reuse the pricey micro for other things made sense.

[@idahofur]

That is so adorable. s-100 buss with a built in storage device. Very nice.

[@jnharton]

Just because there are slots and it's a Z-80 based computer doesn't mean those slots are S-100 compatible.

[@idahofur]

@@jnharton Yea that is true. A few different types and even then. The hardware might be correct. But the slot might be wired a tad different. I have very little experience with s-100 systems. But I know from reading some manuals. Depending on what computer you had. Sometimes you had to change a few jumpers around on the card.

[@soteful9949]

I think I figured out why they got rid of it 38:54

[@bikeforever2016]

I bet the card order follows resistor colour code. Black,brown,red,orange,yellow.

[@esra_erimez]

My dad said he heard, "Paul is dead"... what ever that means.

[@TechTimeTraveller]

"I buried Paul."

[@cherrymountains72]

Now that’s funny 😅

[@georgemaragos2378]

it is a Beatles thing, once of the albums had a cardboard cut out of Paul, the gossip was he died, the bank took a break until a look alike replacement was found and they trained him to be a left handed guitarist It could be true It could be false It could a practical joke due to strong drugs

[@OldPoi77]

I think it is a recording device for older electric typewriters that went in-between the typewriter and the printer to save the text being dictated or as a way for authors to save their work to cassette to be posted to the printers and make copying the manuscripts easier, that's the logical explanation for me.

[@tschak909]

CTRL-Q is DC1 (device control 1) C-R C-S and C-T are DC2 DC3 and DC4, respectively.

[@daemonspudguy]

You sure you didn't buy a very small microwave?

[@MM.]

No, that's the Cathode Ray Dude.

[@daemonspudguy]

@@Freedom4Ever420 what?

[@slincolne]

A couple of things to consider. You have worked out that someone has been inside the box and moved the cards around (not a good sign) and there appears to be an empty ROM socket on the CPU card. It's possible that the unit is not doing what you want as some of the onboard code is missing. I would suggest checking the ROM to see how it is configuring the SIO to confirm Tx & Rx configuration of the serial ports.

[@bloodyhell302]

I strongly believe it's like a tape version of a 1541 disk drive, you hook it up to a (probably proprietary) system and send commands to read and write data and/or do backups. Basically an over engineered datasette.

[@Giepie]

To me it seems like it's waiting for a buffer to be filled before "writing" to tape. Almost like those digital typewriters used to do. So I don't think it merely "randomly" does stuff, I think it's waiting for the buffer to be filled. Ctrl+w (or one of those) might be to write regardless if the buffer is full or not.

[@ugencz8364]

Mystery computers are just like Kinder Surprise eggs... Great video as always!

[@BentonVonKitten]

As memory serves, wouldn't it be 7E1 as an old time standard and 8N1 was the "new" standard for higher baud rate modems?

[@TechTimeTraveller]

@@BentonVonKitten I think you're right.

[@wesley00042]

7E1 is for computers that don't have 8 bit character sets, and 8N1 is for computers that do. Even in 1978, 7N1 would be unusual and could mess with comms.

[@BentonVonKitten]

@@wesley00042 nice, thank you for this!

[@AiOinc1]

6:40 Remember, my friend, the first law of diagnostics! Thou shalt check voltages. 12:54 Just noticed the PC Jr keyboard in the corner and it's kind of menacing

[@HanWelmer]

I have downloaded your ROM dump and started diassembling its Z80 code. Shouldn't take too long. As per the brochure I expect the basic function is to record on tape the serial data passing through the rs232 input and rs232 output connectors. Test method could be to send data in few kbyte chunks at various baud rate settings and check if data is written to tape (observe tape activity) each time the internal data buffer fills up. The brochure states that default mode is record mode. I expect that at power on the device uses hardware default baud rate settings. So no set up would be required. Just try and find out which settings on your sending device (laptop hyperterminal) result in tape activity.

[@8bitwiz_]

21:40 it's best to set flow control to "none" or "off" unless you know you need it. When it's set to "hardware", if the modem control signals (specifically RTS/CTS) aren't just right, you'll get nothing at all. There's nothing worse than when the device is alive, but your terminal program ignores data or sends nothing due to the flow control. (In this case you poked a wire to override it, but I prefer not to have to poke wires when I just need to see any sign of life.) The only downside to not turning flow control off is if you send it a lot of data real fast, it might drop some. But by that point you already know it's alive. As to my guess of how this thing might work, I think you found the control port properly, but I don't know why they thought using random control codes was a good idea. The other port might be the port for the data it is supposed to record and play back. Maybe it was meant to record data over a long period of time for later processing, or maybe it was meant to replay stuff like for repeating a CNC sequence. Or maybe even either one, depending on the customer! It would be cool if you could trace out the card pins to document the bus so that a RAM card or something could be added, but that's so much work for just one existing unit. And I don't appreciate when they make slots slightly different like the one for the serial card, then don't make it obvious which board goes in which slot. Yes definitely it's possible, but just making a proper card that mechanically fits into the slot is a lot of work even before you design the electronics on it!

[@adrianotrindade7925]

I would get an oscilloscope, check clock line of the CPU, check data lines to see if some program is running. And check on the power plug that goes int othe board if all voltages are present. A damaged wire could make the voltage coming from the power supply not reaching the board properly. If you don't know if the processor is running, trying serial comunication can be pointless. Go from the very basics, without assuming anything is working.

[@dansimpson6844]

I used to play with M-80s back in the 70's...🧨

[@moconnell663]

If memory serves, COM1 on your ThinkPad is the irda port. 😊

[@georgemaragos2378]

does it have a built in modem or those "winmodem chips" that could take up the #!, but yes a IRDA port can also be the answer

[@moconnell663]

@georgemaragos2378 I had a ThinkPad 365XD and it lacked a built in modem. I had one of those terrible PCMCIA modems where the phone jack was only as thick as the card and popped out the side. Awful, but still better than a proprietary dongle.

[@bonemar66]

It looks like one port is for tape control, and the other is for data. Ctrl-Q seems to be "cue"; Ctrl-R might be "replay", and that fast forward you noticed might be a scan for data tones on the tape? Save something on your PET datasette and see if this thing can "see" anything on that tape.

[@TechTimeTraveller]

I didn't think about it maybe looking for tones and not finding them. Making notes for a future run at it again.

[@patrickelliott2169]

Ctrl-r might also be intended to be "run", other control codes after might do other things "only" when already in run mode. In fact, it might be like a Commodore load command, you hit "run", then thpe in a short code, which defines the label on the tape to look for to load and run, but it never "sees" it, so it just runs out the tape trying to find it. Mind, this is mostly me talking out of my ass, based on really limited info on how like.. maybe all of two computers handled tapes.

[@8bitwiz_]

Ctrl-r could also mean "rewind", if you over-think it enough.

[@emuhill]

The PET very likely uses different tones to what this device uses.

[@uni-byte]

How to tell people you are Canadian without telling them you are Canadian? Use a MasterCraft meter!!

[@TechTimeTraveller]

Dead giveaway. Damn.

[@emuhill]

As an American, that wouldn't tell me anything. Nor would I even care for that matter.

[@uni-byte]

@@emuhill Exactly. I know it surprises most Americans, but there really is a "rest of the world" and it's 24 times bigger than the US.

[@emuhill]

@@uni-byte 1. What meter you use doesn't mean anything to me nor am I going to care about it. 2. I DON"T GIVE A DAMN WHERE YOU ARE FROM! 3. There is no nation on this planet that is so special including the US that it should even matter if someone is from there. Essentially you are saying "Look at me. I am using so and so meter so I am Canadian!" Meh. Big deal. 4. "I know it surprises most Americans, but there really is a "rest of the world" and it's 24 times bigger than the US." I already know that. 5. You're meter isn't likely to mean much of anything to anyone outside of Canada or at the most outside of the British Commonwealth. Enough said.

[@uni-byte]

@@emuhill Triggered much? If none of this means anything to you why are we having this .. conversation? Just to be clear, it was an inside joke and not meant for you. Just to be doubly clear, I couldn't give a flake of skin off a gnats left ass cheek what you opinion on this is. Got it?

[@chasonlapointe]

Very cool, I love a deep dive troubleshooting video!

[@HanWelmer]

My reverse engineering would be helped with the following: 1) Can you confirm a 4K ROM is present at addresses 0x0000..0x0FFFF? 2) Can you confirm RAM present at 0x1800..0x1BFF and its size (1 Kbyte)? 3) Can you find out IO addresses used by components (Z80 SIO and Z80 CTC) on communication board?

[@NotAvailable-b6d]

Looks like an Embedded Computing System .. Popular in the 70's and heavily used by the military and industrial processes .. The Key characteristic is no means for user input or output .. The actual programing is done on a mini Computer like a PD11/34, and once debugged burned into the ROM .. Additional Code could be on tape, but not likely due to low RAM .. Think of a repetitive process like weaving a complex pattern / picture .. The for example if serial output controls a weaving machine's pattern .. The tape contains the pattern code which would make no sense to a human looking at it .. The weaving machine would control the unit to reset it and read from it, once the pattern is completed it resets and does anther one .. Where and how this was used is anyone guess .. A lot of this stuff was very custom for the actual equipment and process ..

[@zbradbell]

you can tell if the cards are in the right slot by the color code!

[@Matt47247523457]

The designer must have worked at HP

[@bikeforever2016]

There's a us patent for a tape mechanisum 3724780 for metrodyne, so it seem like tape drives were their thing.

[@ericswanson2527]

I believe it's using the same control codes as a teletype paper punch/reader. ^q - start read, ^r - start write, ^s - stop read, ^t - stop write. Watch out, a lot of terminal software will interpert ^q and ^s as software flow control.

[@TechTimeTraveller]

I think you are on the money. I found a tape that was in far better condition than the one I was using in the video and it runs much smoother. I also tried 1200 baud, 7E1 and it seems to respond better, although it still returns gibberish to the terminal. But I did try your idea.. I hit ctrl R to start a write.. sent data.. and then confirmed stop write returned me back to being able to do the read functions. Before when I'd hit ctrl r i couldn't figure out how to get out of write mode. I just can't figure out the read mode and what it's supposed to do exactly when I hit ctrl q. When I did that and it hit a part of the tape recorded by another computer, it started spitting out nonsense characters onscreen, acting like it was reading something.

[@ericswanson2527]

@@TechTimeTraveller It may not have transport controls (fast forward/rewind). Try with a leaderless tape (dictation or computer tape). Write stuff to it, then pull the tape and rewind it with something else, then try to read what was written.

[@TechTimeTraveller]

@ericswanson2527 That's exactly what I tried after I wrote my msg. I rewound to the beginning, and then put it into record mode and sent a plain text file filled with As. It whirred away, sometimes doing like a Coleco Adam does.. stopping, back forth then forward again. Ran to the end of the tape. I then rewound, put it back in and tried to read. It seems to read what I'm calling a 'block' at a time, and it fills the terminal screen with text. But not As As expected. Often just rows of + signs or sometimes an unintelligible repeating pattern. I adjusted every terminal setting I could find. It does not respond at all above or below 1200 baud, so I think that's the correct communication speed. But I tried like 7E1, 8E1, 7O1.. every variation possible and for most its basically the same gibberish each time. Except if it's 8e1 I might get these random ansi block characters instead of +

[@Andy-fd5fg]

Are you sure both connectors on the back are serial ports? Perhaps one is a data input of somekind? Maybe the Card with the Red tabs is some sort of DAC? The tape deck sounds like it needs a service

[@TechTimeTraveller]

@Andy-fd5fg I think J2 is a data input and J1 is rs232 compliant and used for control. In documentation I've found they explai how a computer/terminal connects to J1 and drives the system. On other models they actually have a keypad on the front and those gives you direct control over the internal computer as well as the drive. I think on balance its mainly a computer driven cassette data acquisition device, with the option of turning it into a full blown computer, still mostly aimed at that purpose, with available expansions.

[@briangoldberg4439]

It seems to me it's likely a tape data storage device, and you would need to figure out the commands to store and retrieve data to use it. This has likely been mentioned already, so I'll just say that I add my vote to this explanation

[@tschak909]

those audio tones are phase shift keyed. Am willing to bet you could sample those and decode it as a fairly straightforward PSK signal, sans-carrier.

[@wytsfrevsf]

may be a data recorder, when you got it running it seemed like it was writing data to the tape as you typed, maybe recording aircraft system data over TTY to tape

[@eben_the_great]

It might be assuming the tape is specially formatted with data, and the endless seeking is it scanning until it finds ,

[@davidtwist3659]

The tape drive could be digital and the head reads two tracks, one data and the other a clock. The clock is used to tell the computer where the data is. The tape has a header like directory of the data stored. The clock track is high precision so the tape speed can be adjusted whilst reading or writing data.

[@davidtwist3659]

Also the digital tape have pin holes at the start and end of the tape. So on start up the tape will run till the start if tape is found. If not the tape will just run fast forward till it finds the start of tape.

[@rogerioayres]

The RS232C settings are wrong. Obviously the connection with m-80 was stablished, but that weird characters on the hyperterminal reveals wrong parameters on the RS232C. Look at hiperterminal status bar. Those modifications that you made do not had applied actualy. Try others configurations like 1200-7-N-1 or 1200-7-o-0, 1200-8-P-1 etc... Make sure that parameters realy was applied (monitoring in the hiperterminal at there status bar).

[@TSteffi]

I would recommend Teraterm for such things. Much better terminal emulator

[@SimonZerafa]

Its a process or similar data recorder so a serial input goes in and is passed on to kther equipment while being recorded? 🙂

[@soteful9949]

Can it run Crysis?

[@DeadKoby]

By the way it's operating, it seems like it might be a flight recorder thing.

[@asteroidrules]

Never heard of this machine before, but now I wanna see it working just to figure out what the previous owner was using it for.

[@vilaintrolltrollinsky8007]

Look like a data recording device. Like a Black Box.

[@TechTimeTraveller]

Damn. Totally missed a good skit opportunity there. Next time.

[@BrainSlugs83]

Reminds me a lot of the Commodore 1541 Disk Drive. Technically it's a stripped down, low memory, 6502 computer... with a serial interface... -- but... you used it from the main computer, not directly. Usually the main computer would have something in ROM that would translate simple commands into a sequence of commands that the drive itself could execute and do something with. It seems like some specific codes you use advance the tape by just a tiny amount, and others jump it into fast forward -- I'm guessing, that the tiny amount command would be spammed to the device to advance the tape, then another command to read back a value then advance the tape again, then read back another value, etc. etc. -- the fast forward command you keep getting is probably not one that it directly used. (Unless it's playing at a very normal speed, and it's just squeaky?) -- The random character is the value is read back from the tape. Then you want to advance it by one tick, then read back the next character, etc.

[@Jerrec]

Maybe it records the stuff that is transferred to it via the 2nd serial port?

[@kepanoid]

Did you ever end up going through all the settings in your terminal emulator program? Like turning off the hardware handshake which you explicitly showed as "on"? *Every* reasonable baud rate? The thing doesn't seem to be an automated data recorder, since it needs some input. That input doesn't seem to come from a tape automatically, either. So it clearly needs some user interaction.

[@leeselectronicwidgets]

Scope the RXD and measure what the period is on the strange character it's returning. In late 70s it could be 300 baud or even 110!

[@NiallWardrop]

It's been a long time since I messed with this stuff but my recollection is that wrong baud rate you get nothing at all, wrong data format gives wrong characters.

[@Brian_Of_Melbourne]

In fact the question is why DIDN'T you START by scoping the 25-way connectors? This would establish which pins are being driven (Tx) and by observing the output at power-up or reset establish if anything is being transmitted and at what baud rate. You might also establish which pins are inputs, a CTS type of input might need to be asserted to allow characters out of the device.

[@stevec00ps]

You said to use 7 data bits but it says 1200-8-N-1 on the status bar of Hyperterminal. I'd try disabling flow control too, or connect to a scope to work out the baud rate etc.

[@AlexDindikov]

Is it possible have cp/m with tape from this computer?

[@sebastian19745]

Why do you have to assume and poke so many things? I see the serial card with the line drivers (what are they, MC1488/MC1489?). Just follow the outputs to the DB25 connector and see were are those Rx and Tx pins. You know that Tx should be at pin 2, if pin 2 is an output of MC1488 then pin 2 of DB25 connector is Tx. If not, check if is an input for MC1489, then is Rx. I had a computer, Z80 based that booted in BASIC when a key was pressed on its keyboard, displaying the image on a TV set. But, when it received a character from an data terminal connected to its RS232 port, it used the data terminal as in/out console, not displaying anything to the TV and not accepting any inputs from the integrated keyboard. Maybe it expects to receive something via RS232. That ROM is 2k only, maybe is a loader only and it expects a tape to be loaded in the RAM at boot to load some OS from there? Also, there is the socket for a second EPROM, may be there a option to insert a programmed ROM with the OS (maybe a monitor or a test/debug ROM, anyway something small because the EPROM seems to be max 1-2K )? Also, it maybe just write on tape the input data when the serial buffer is full (like at 52:20, that "ocassionally" writing on tape), being so, similar with C64 floppy drives. Btw, what you did at 52:20, did it writed something on tape? Edit: I believe that the last version seems to be the most probable, a glorified tape recorder. And, based on the brochure, I guess that this is the remote controlled version of that showed in the brochure. Control-P looks like reset (SHIFT BACK) and Control-R looks like Tape ON (Write NO SHIFT).

[@georgemaragos2378]

Hi Interesting device. I am glad you traced the power on the card and sorted out the + and - voltage traces - i would have not thought of that. However i would not use that 25 to 9 pin adapter, you are assuming it is using a hays standard or more modern ibm standard of serial port wiring Maybe the volt meter should have been used on the 25 pin port with the tape playing to see if there is any +12 or -12 voltage coming out of any of the 25 pins ( well 50 pins as you mentioned there are 2 off ) Then the same with the oscilloscope Initially I was guessing one port is for a screen and the second for the tape back up, but you mentioned the eprom dump shows nothing that sophisticated - but if it was a screen output that would also be on a a simple serial out I was actually suprised, you did not cut and paste some text into the hyper terminal software and see if it stored the data / keystrokes and the tape unit attempted to save the transmitted characters But your data recording playback did not have any different tones that would have been produced for each different key press It is a shame the machine is so well built that it did not have a simple description of which slot each card goes into on the card or even a texta or sticker on the card slot edge or backplane slot saying red/brown/yellow etc Unless the serial parameters are exact the device would not understand the characters and not work as designed, however the fact that the hyperterminal only ever showed character on screen that was a result of your key press , and never any characters that were generated by the tape drive could suggest that the 25 to 9 pins adapter may not be correct, some important pins may need to be connected as 25pin to 25pin - this happens with say cash register comms - there is a scan code or maybe a Control G to trigger the drawer open, other serial printers use a spare pin for special feature - the "paper out" is a example as different printes used different spare pin to report back - this is why some printer you had to use the factory cable not a generic serial printer cable I dont think it requires additional voltage via the serial cable, it seems to "quick forward" on Ctr-Q so no real need for extra power - some items need a +5 or -5v for options to be sent in the cable - security door loggers are a example, we had one in a building i worked in, it used standard serial and all data was captured via dos telix software on a Pc ( it saved the buffer every so often 2k ??? ) , any way , you could actually unlock the door with a keypress on the PC, as it relied in a +5v signal on a pin to send back to the door lock and unlock it

[@davidholloway1042]

I was poki g around and found a NASA pdf. I am unsure if it will help. They do talk about the Memodyne.

[@TechTimeTraveller]

It might! I wonder if it's the same I was looking at.

[@jeromes624]

What if the default is load on power. The serial communication is saved onto the cassette. The cassette now holds the software to run.

[@jldwolfe]

I am far from any kind of expert but my guess is some sort of automation device. Enter in a series of pulses that are recorded on the tape to play back and trigger something like relays and such.

[@penfold7800]

Have you tried just plugging in an old dot matrix printer into the serial or parallel socket? The other socket could be for data gathering cables. And the unit itself might just be a processing unit that outputs analog results of probes to a printer and does a digital backup on to the cassette. The cassette can then be used on another computer with an interpreter program running. I would look up old meterology articles like for seismology or weather stations rather than aerospace specifically.

[@vanhetgoor]

The buttonless cassette recorder is interesting, I have seen something like this before in the Philips P200t, the cassette recorder unit came from Japan. It was possible to record one programme and delete a programme from tape it does not matter where it is, even if it was between two other programmes. Try to keep this intact and complete. I guess this is more advanced then you think.

[@TheMicro4]

This is the kind of thing that is probably laying in government storage cabinet somewhere

[@uni-byte]

I like your opening music. Where'd ya get it?

[@TechTimeTraveller]

Epidemic Sound

[@uni-byte]

@@TechTimeTraveller I guess I could have looked in your description (LOL) but thanks for your response. Much appreciated.

[@Aeduo]

Wonder if that's one of those 9(?) track cassette-style tape systems like a Coleco Adam.

[@grinderkenny]

Being a old serial unix guy.. seams to me the wrong baud rate. May be able to look the serial card chips up and figure out the baud rate. May be some jumpers somewhere. Just an idea.. Probably not much help.

[@Giepie]

Couldn't it also be flow control? 99% of the time I needed to turn it off (back in the day)

[@grinderkenny]

@@Giepie thers not enough data coming thru to be flow control. Easy way to find out is to disconnect the flow control pins

[@nalinux]

It sounds like an over-engineered mouse repellent :)

[@bloodyhell302]

In hindsight, it could be some sort of stenography recorder.

[@Dinnye01]

So you swapped a chip on the serial board and then held the adapter in the air instead of plugging it in... I was close to screaming at my screen. Please put some method into that madness, especially if you have a scope!

[@TechTimeTraveller]

Based on my experience with computers that use serial terminals, I'm used to seeing the TX light activate briefly as the system sends out a console prompt. Because it had not been working at all and because I wanted to quickly show viewers what the result was, I held the breakout device up to the camera to quickly assess of anything had changed.

[@snakezdewiggle6084]

@TechTimeTraveller How does your "beakout" thing show Negative going Pulses/Data, HI/Z States, etc.? A single two wire serial connection has four channels, its Binary right.?!. Truth Table it.

[@jnharton]

@@snakezdewiggle6084 It's probably a breakout mostly in the sense that you can control how the serial signal lines are connected. That can mean disconnecting a signal altogether, routing it to a different pin than usual, grounding it, or pulling it high. It may also facilitate turning a straight through cable into a null-modem one or vice versa (especiallly routing of the Tx, Rx lines). Putting LEDs on the line is a crude form of checking for any signal at all (LED on, LED off, LED pulses on/off). It only tells you that something is definitely happening. There are many, many possible configurations of a serial port/connection. Breakout boxes that work this way were extremely common back in the days of dumb/smart serial terminals that connected to a minicomputer ir mainframe.

[@jnharton]

@@snakezdewiggle6084 A two-wire serial connection would be exactly one bidirectional channel (or two unidirectional ones).

[@DAVIDGREGORYKERR]

What about having the card with the Red grips as the first card on the left then the card with the Orange Grips between the card with the red grips and the card with the Yellow grips.

[@HanWelmer]

Given the z80 code at 0x005F..0x0100 and the firmware default configuration data at 0x0300..0x035A I assume the SIO is connected at port 0x10A..0x13. And that port B is set up with 8 data bits, 1.5 stop bits no parity and X64 clock rate. I haven't figured out yet the CTC configuration and assuming it drives the SIO tx/rx clock I have no clue what the bit rate is.

[@marksmith9566]

Tape drive sounds ILL!

[@noscwoh1]

Why not fix the cassette mechanism first? It sounds like it's fighting itself. Clean the pinch roller, oil the capstan, replace any belts, all that Techmoan stuff. :)

[@TechTimeTraveller]

@noscwoh1 it's actually the tape. I later found another and the grinding went away

[@AlT-vt3gb]

Is it just a tape drive for a computer maybe?

[@jnharton]

Probably not given the label says "Cassette Computer".

[@tolentarpay5464]

A trick I saw on The 8-Bit Guy: set it up in a lightproofed room with a camera, then turn power on & look for shorts. Worked pretty well...

[@TechTimeTraveller]

Think I've seen that trick..

[@AndrewFremantle]

The inconsistent results and garbage coming back make me suspect your serial port configuration is incorrect - probably the wrong baud rate.

[@TechTimeTraveller]

I did try literally every setting possible although for video length reasons I didnt capture all of that. 300 up to 19200, different terminal emulation, bits, stop bits etc. It really did feel like a baud rate problem but above above 19200 it produced nothing and below that just garbage. I suspect it was never meant to communicate with a human operator. The fact that it responds to the control sequences durgadas311 determined were there, only at that baud rate, suggests probably we had it right at 1200 and something else is at work. Wish I could find proper documentation.

[@Brian_Of_Melbourne]

@@TechTimeTraveller So, why DIDN'T you START by scoping the 25-way connectors? This would establish which pins are being driven (Tx) and by observing the output at power-up or reset establish if anything is being transmitted and at what baud rate.

[@TechTimeTraveller]

@Brian_Of_Melbourne Because I am an enthusiast, not an EE. What is self evident to those who are trained or naturally talented with these things is not always obvious to someone without that expertise. I just began learning how to use my scope recently. This channel is not intended to be educational per se - just a hobbyist learning as I go. That said, I always welcome helpful comments and try to learn each time I approach another repair.

[@garrettzuhoski]

Blaze it up

[@SyldabiaHacks]

You need read eeprom disassembly and read to know how it works.

[@Clancydaenlightened]

3:25 just like an Atari floppy drive is pretty much most of an atari 2600 just throw a tia chip in

[@Clancydaenlightened]

It's not the Atari or commodore doing the Dir The floppy drive does dir and then sends a small preformatted readable list to the computer to spit on the "gpu"

[@Clancydaenlightened]

Wen you modded your floppy drive with a cmos 6502, new eeprom and ram expansion....fast clock speed upgrade Get 128kbyte/sec transfers over the Sio port, with built-in cache and floppy ramdisking

[@Clancydaenlightened]

That's why unlike a c64/128 You just put the floppy in drive 1 Power on drive, then power computer Don't even need to type, if boot sector is right, autoloader Atari 8bit was around 1977 but got to market in 79 started prototypes around 1975

[@marksmith9566]

S100 Bus backplane?

[@50shadesofbeige88]

Waat? It looks like a power supply or something.

[@RyanDanielG]

nice

[@josephlunderville3195]

8:45 Line driver/receiver

[@tschak909]

it's acting like a remote key to tape machine.

[@peterkaldenberg2812]

a scope will help you

[@Jordan4Ibanez]

I'm only in 40 minutes but my guess is Query (start of tape), Read. But I suppose I'll find out soon lol

[@G7VFY]

You keep fiddling with different parts and never resolve any. Start with comms, 7 bits, 1 stop bit and no parity is the place to start. This appears to be a data-logger so it will be recording received data to tape for later analysis is not unusual,

[@TechTimeTraveller]

@G7VFY I'm afraid my editing skills are still a bit choppy. I actually did go through pretty much every combination of data bits, stop bits, parity and handshaking options off camera... even forcing hyperterminal to make the input 7 bit. Nothing got a result unfortunately.

[@pikadroo]

Hey how about a video on alternative sites to ebay. I just got roasted and lost 15 years at 100% positive cause of a $2.99 used router. I am a sinner now and must be dealt with according to the buyer. Ya know, off with my head cause I forgot to put the power supply in in the damn box.

[@Dron2203]

😁👍💪🧠👏

[@F40PH-2CAT]

Does it run Chrysis?

[@TechTimeTraveller]

I think it would run FROM Chrysis

[@gaborv.6502]

A nuke missile launch computer (casette = target data) xD

[@davidmckendry4491]

Will it run doom?😂😂😂😂😂😂

[@snakezdewiggle6084]

Do you know how long (minutes) it takes a Z80 to load an OS.!? How do you feel about the paradigm of Patience.! 6 seconds was longest period between "reset reset reset reset". I think you screwed yourself over with q bunch of other bad habits also. Assumption should Remain in the dictionary.! Not on the work bench.

[@kaitlyn__L]

Given the videos about using The Digital Group's boxes, I'm thinking he does know... (though I do agree this video feels a bit more scattershot than it could, indeed more than they usually are)

[@snakezdewiggle6084]

@kaitlyn__L Hello kaitlyn__L. Yeah a bit rough shod for sure. I'm new here. Saw Z80 and knee jerk clicked. Zilog fan boy. Yes tragic, I know.😆 Now! the obligatory Z80 Trivia. Did you know the 👉Z80 has a 16 bit register.!👈 😲 One clk in, one clk out. Very tasty 👍 Have you seen the .bin file yet? I think its broken..

[@alexhajnal107]

27:15 _"It seems to be very random"_ Check the power rails. They may be (intermittently) sagging due to bad caps. (A 'scope would be ideal for this as a multimeter may not have sufficiently fine-grained time resolution.)

[@samkg1964]

.214 .214 .214 .214