From 29f3bf1e70bad3ce71c6bd7fa81d5a0dfc6a706f Mon Sep 17 00:00:00 2001 From: Virgil Dupras Date: Tue, 3 Nov 2020 16:54:30 -0500 Subject: [PATCH] doc/hw/sms: adjust ROM hacking instructions Previous instructions would only work with an AT28C64. Now, it also work with an AT28C256. --- doc/hw/z80/sms.txt | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/doc/hw/z80/sms.txt b/doc/hw/z80/sms.txt index 91d6aec..ab60aaf 100644 --- a/doc/hw/z80/sms.txt +++ b/doc/hw/z80/sms.txt @@ -8,8 +8,9 @@ had a z80 system for compatibility! This makes this platform *very* scavenge-friendly and worth working on. -SMS Power[1] is an awesome technical resource to develop for this -platform and this is where most of my information comes from. +SMS Power[1] is an awesome technical resource to develop for +this platform and this is where most of my information comes +from. This platform is tight on RAM. It has 8k of it. However, if you have extra RAM, you can put it on your cartridge. @@ -18,8 +19,8 @@ have extra RAM, you can put it on your cartridge. * A Sega Master System or a MegaDrive (Genesis). * A Megadrive D-pad controller. -* A way to get an arbitrary ROM to run on the SMS. Either through a writable - ROM cartridge or an Everdrive[2]. +* A way to get an arbitrary ROM to run on the SMS. Either + through a writable ROM cartridge or an Everdrive[2]. # Hacking up a ROM cart @@ -36,13 +37,20 @@ SMS-related stuff, I recommend the 32K version instead of the 8K one because fitting Collapse OS with fonts in 8K is really tight. +The ROM cartridge follow regular ROM pinout, which means that +A14 are just under VCC, where WE is on the AT28. We need WE to +be perma-disabled and A14 to be properly connected. + 1. De-solder the ROM 2. Take a 28 pins IC socket 3. Cut off its WE pin (the one just under VCC), leaving a tiny bit of metal. 4. Hard-wire it to VCC so that WE is never enabled. 5. Solder your socket where the ROM was. -6. Insert Collapse OS-filled EEPROM in socket. +6. With a cutter, cut the trace leading to A14. +7. Wire A14 to the trace just under WE (which doesn't actually + touch WE because we've cut the IC socket's pin). +8. Insert Collapse OS-filled EEPROM in socket. As simple as this! (Note that this has only been tested on a SMS so far. I haven't explored whether this can run on a megadrive).