Z80 Retro #65 - Alternate FLASH and SRAM chip options for the Retro!

[@johnhansen4794]

Not only good information on this project, but also this whole series continues to be a course in how to think about these issues. Really digging it.

[@JohnsBasement]

Thanks!

[@JyskMaker]

Nice serie, want to make one to. Is it ok to uses LS and not HC?

[@JohnsBasement]

For most, yes. But not for the nand gate in the reset circuit. And possibly not the latch that drives the SD card bits.

[@JyskMaker]

@@JohnsBasement Can you say way?

[@JohnsBasement]

@@JyskMaker reset needs schmitt. HC or HCT for SD signals to get right voltage.

[@kenpeter3767]

Vaguely recall as a child rewriting and assembling by hand almost the whole Xerox820-II CBIOS just to make extra space for a track buffer. Maybe never fit the whole track and had to settle for 512byte sectors that CP/M saw as 128, and 1:1 interleave? Fewer gaps allowed more storage, and faster. ROM was shadowed to RAM and not write protected, so could do tricks like that if one could punch a big enough hole. These days would probably use non-volatile 35nS parallel MRAM for both. Big enough I could fit the whole floppy too. Can't remember Z-80 or CP/M well enough to pull that off anymore. Xerox was a clone of Jim Ferguson's Big Board, if that might be more familiar. I see only now your #62. My comment might also be relevant to that.

[@JohnsBasement]

Sounds like good times!

[@SimonJackson13]

They want you to OCD route the 2 selects from the bank decoder to the pins to get 6 images in ROM. An eight joke irritation. :D

[@JohnsBasement]

When it boots, there is garbage in the bank latch.

[@SimonJackson13]

So it needs about 128 bytes of common code in each ROM to springboard to the first, and then any other. The lack of a subroutine stack while ROM execution happens is perhaps the biggest issue with ROMs in the design anyhow. The jumper for ROM 2 though is a nice feature.

[@JohnsBasement]

@@SimonJackson13 yeah, start the same would work. I'm not sure how it'd be useful though without any ram at all.... Maybe read a keyboard select command to pick which of the images to copy into RAM?

[@sparkybrit]

Discord? What channel?

[@JohnsBasement]

The one in the video description. 😁

[@7alken]

please, how to join the Z80 retro discord, the invite is invalid...

[@JohnsBasement]

The link in this video's description worked for me. What link did you use?

[@7alken]

@@JohnsBasement its weird, incognito window works... excuse me, I am not using discord much, will solve it