So, spend a few hours desoldering a Konami-1 bootleg replacement, and then find that someone else has done most of the work of making a schematic already.
The board itself
Seems there are still some questions regarding the extra pins (Konami-1 is 42 pins rather than 40 like a 6809e) and interrupts. Maybe some examining of boards with builtin Konami-1 replacements like Junofirst and Gyrus is necessary.
As far as I know Circus Chalie and Ropeman use this daughter board too.
Swapped the switching FET to an open collector 7406 (I didn’t have an LS handy) and I was able to reduce the delay in the read considerably.
Reading the directory from the SD card works which is cool.
As the SD/FAT code needs to run in the System24 bios, it all needs converting to 68k assembler. After a few evenings work, the code to interface to the sd card is written but still needs debugging on real hardware. FAT16/FAT32 (or maybe just FAT32) code to be converted next.
The beauty of having the code working in C is that I can just replace each function with it’s assembler version and test each one. (after realising I needed to create some trampoline functions to convert the stack passing method to a more typical assembly call method.. unless there’s a compiler function to use register passing.. I wonder..)
After spending a ton of time researching sdcard interfacing, perils of voltage shifting and with the help of Charles MacDonald getting the Genesis C compiler working on System 24, I have successfully read a file from a SD Card. whoo hoo.
This is only proof of concept as the hardware is very slow receiving data and all the C sdcard and fat16/32 code will need rewriting in assembler. Hopefully a change from a FET to a 74ls05 will improve the speed.
The natural progression for Sega after the popular system 16 and system 18 games, was system 24. Higher resolution graphics meant using a medium res display and needed more memory to store the graphics data. Sega’s solution was to use a cheap medium instead of expensive eproms. Over 8 megabits of data…. Floppy disks! How can it fail. But wait, floppy disks can be easily copied, so Sega continued the usage of their FD1094 security processor.
Move forward 20 years and arcade collectors have a major pain. FD1094 batteries failing and disks either getting lost, or damaged from overuse.
A cheap repair/fix solution is needed.
Putting together a System 24 USB adapter, modified System 24 bios and a disk server program running on my PC and voilà, nice fresh disk images can be written using the System 24 hardware itself.
Modified Bonanza Bros disk running on a Dynamic Country Club rom board
My System 24 Scramble Spirits cabinet buried under stuff
At the request of a friend I was asked to fix the inverted screen issue with Athena.
An hour or so at the hands of the MAME debugger and a couple of false attempts the resulting patch is a simple two byte change to the rom.
In rom up02_p4.rom change these bytes. (actually, the patch swaps them around)
$029e to $48
$02a4 to $3e
Burn a new 27c128 rom and its done. Since we are swapping two bytes, the checksum doesn’t change.
Edit: Tested on a real pcb. Works perfectly as expected 🙂