stas2k / galspanic

X68000 RAM Expansion

GALSPanic - X68000 SRAM Expansion

This repo contains Kicad sources for a Static RAM expansion board for Sharp X68000 personal computer. Please use latest git version of kicad to open the project, or version >6.0 once it gets released.

Design

The expansion is implemented using 2MB static RAM chips to make the design simpler. Address decoder is implemented using a ATF22V10 GAL chip. Source code for it is available in gal/ directory.

Board dimensions are taken from the midiori project.

The board can support up to 10MB of memory and assumes you already have 2MB built in.

A fourth address line is routed and the board can support 1MB systems by masking half of the first memory chip. However, the GAL equations are not written for this case. Let me know if you have such a system.

Compatibility

Following systems have been reported to work:

• Super
• Expert
• ACE
• XVI
• Pro
• 68030

GAL Equations

You can compile .pld GAL equations using GALasm.

Board production

I use JLCPCB with the following options:

• PCB Thickness: 1.6
• Surface Finish: ENIG-RoHS
• Gold Fingers: Yes
• 45°finger chamfered: Yes

galspanic's Issues

Unable to open the pcb with kicad

Hello there,

thanks for this project , i wanted to check the pcb , but i'm unable to open it with KiCad for windows,
Tried the latest version stable 5.1.7 , nightly build and a older version from May 2020. Do you have a link to the version you're using ?

thanks in advance and best regards

DTACK Issue

On the schematic DTACK is Pin 1 on the GAL where as in the PLD file its is Pin 23. Since it is an output it can't be on Pin 1.

I noticed this after assembling a board with 3 SRAM chips and testing in an ACE with a Sharp 1 MB expansion on the internal memory expansion header. I worked around the issue by cutting the link on the "1 MB" jumper and adding a wire between the middle pad of the jumper and Pin 1 of the GAL. I tested with a program found somewhere called "mtest.r" which passed.

I also felt that the GAL was getting warm from driving DTACK as push-pull rather than open drain so I added an open drain buffer. It is maybe less warm, but I don't have a way to measure well. It worked with and without the buffer so this may not be an issue. I think using the tri-state outputs on the GAL should be able get the same effect.

Can you add a BOM

If you can add a BOM to the release files I can make it without having to work out what version of kicad makes those file extensions.

10Mb Memory Expansion on X68000 Pro System

Hi,

I have made a couple of these expansions, as the project is very promising.
Unfortunately the first tests did not recognize the memory expansion.
The setup is as follows:

• Gals Panic! Expansion board fitted with 5*2Mb SRAM
• 1Mb RAM masking off
• 4,6,8 and 10 Mb switches on "ON" position
• Standard .pld equations (the one published, which I compiled)
• X68000 Pro with 2Mb internal Expansion

Once the X68000 boots, i execute switch.x and configure 10240 Kb, save the settings and reboot.
Once rebooted I get a message if I want to switch back to 2Mb.

I tried SSF2 and it does not even startup, so it seems that for some reason the memory expansion is not detected.

Am I missing anything?

Thank you.