Hardware VGA Episode 02: VRAM (and other stuff)

This episode of the Hardware VGA series covers adding 8 KB of video memory to the display controller.
All of the schematics, code, GAL equations, etc. are available on the project's Github site: github.com/daveho/HW_VGA
I didn't explicitly cover the GAL programming for control signal generation in the video, but you can see the equation file here: github.com/daveho/HW_VGA/blob...
Contents:
00:17 Introduction, outline
00:50 Responding to feedback on Episode 01
02:36 Hardware changes
05:51 PCB space budget
06:40 VRAM module design overview
09:23 Prototype VRAM module
12:57 Conclusions

[@RayBellis]

I'm glad to see my suggestion for sending the VIS signal into the multiplexor's E line worked! :D

[@davehohacks]

Thank you for pointing it out! Always nice to reduce the part count.

[@sergatmel8242]

I'm watching this project with interest. Thank you.

[@davehohacks]

Glad you're enjoying it!

[@AjinkyaMahajan]

You Seriously did wire-wrap those ICs. Hats off to your patience

[@davehohacks]

I find point-to-point soldering to be therapeutic somehow.

[@DirkJMartens]

Very interested in the VGA card. Especially how you will interface the software with the hardware.

[@davehohacks]

I think the software should be fairly straightforward. The only real complexity will be the bank switching, so the software routines will need to set the bank depending on which character or attribute they need to access.

[@ChipperClipper1]

You're really smart and this is a well put together video. I wonder if you could create a dumbed down version of this video to appeal to a wider audience.

[@davehohacks]

If you go way back on my channel to the early videos in the 8-bit computer series, there are some videos that go into more of the basics of address and data busses, bus control signals, etc. The nice thing about dual port static RAM is that it works exactly the same way as "normal" single-port static RAM, you just get two independent interfaces. Static RAM is very easy to interface. Also, definitely check out Ben Eater's videos on building a 6502 system if you haven't already. He does an amazing job of explaining things.

[@AppliedCryogenics]

I haven't checked yet of course, but have been wondering if the 6309 bus cycle in my project leaves enough idle time to externally access the fast system SRAM without having to slow the bus clock down from 3.57MHz..

[@davehohacks]

I guess when E is high the 6309 isn't accessing memory, so maybe your external device could sneak in then?

[@cbmeeks]

I need some of that wire. Do you remember what gauge it was? I have wire-wrap wire but it's way too thin for soldering (at least a lot of soldering).

[@davehohacks]

If you search for "UL1423" on AliExpress, there's a listing from a vendor "FreeBoom". I ordered the 26 AWG variant. I'm not sure if it's really 26 AWG, but it's definitely thicker than normal 30 AWG wire wrap wire. I've found it to be excellent for point-to-point wiring on protoboards.

[@cbmeeks]

@@davehohacks Thanks!

[@DirkJMartens]

I dont think this was wire wrapped. If i understood Dave well, he used wirewrap-style wire and did P2P soldering. Real wirewrapping would be actually be faster. I wirewrap a 100mmx160mm eurocard-sized pcb with 20 or so ICs in 6 to 8 hrs.

[@davehohacks]

Yes, this is just point-to-point soldering. I have done some wire-wrapping in the past. My only real objection is that wire wrap sockets are expensive.