Assembling a 1 MB ASCII MegaFlashRom with 32 kB SRAM using the LZ93A13 mapper

 

DIY – Assembling a 1 MB ASCII MegaFlashRom with 32 kB SRAM over an LZ93A13 mapper

 

Hello everyone!

 

The MSX ASC8 (ASCII) ROM mappers can control up to 1024kB of cartridge memory with chip LZ93A13 (ASC1) or up to 2048kB with chip M60002 (ASC2), when in 8 kB mode (and twice the size in 16 kB mode). Several game designers used this Rom mapper.

 

So, this DIY project will use a 1 MB (8 Mbit) KOEI cartridge with SRAM to create a 1024kB MegaflashROM with a 32 kB SRAM

 

List of components:

1) MSX cartridge with LZ93A13 (ASC1) or with the M60002 (ASC2).

2) Optionally, an MSX cartridge with a SRAM (CXK58257) and battery backup already connected.

3) 1 mini switch (2-pin) to turn on/off the MegaflashROM

4) 2 flash memory - 512 kB (am29f040b) – optionally, you can use only 1

5) 1 decoder 74HC139 (or LS139) to decode MA19 (B6) to switch between the flash memories

6) 1 resistor of 4.7 kΩ

 

The connections will be made from (both) the flash memory to the MSX bus and to the LZ93A13:

1)  A0 to A12 of (both) flash memory connected to the MSX address bus

2)  A13 to A18 of (both) flash memory connected to B0 to B5 of the LZ93A13 (or M60002)

3)  D0 to D7 of (both) flash memory connected to the MSX data bus

4)  /WE of (both) flash memory connected to /WR of the MSX address bus

5)  /OE of (both) flash memory connected to /OE.00-7F (pin 8) of the LZ93A13 (or M60002)

6)  /CE of flash 1 to pin 5 (/Y1) of the LS139 

7)  Optionally, /CE of flash 2 to pin 7 (/Y3) of the LS139

8)  /SLTSL of the MSX address bus to pin 1 of the switch

9)  Pin 2 of the switch to pin 1 (/G) of the LS139

10) Resistor of 4.7 kΩ between VCC and pin 1 (/G) of the LS139

11) /RESET of the MSX address bus to pin 2 (A) of the LS139

12) B6 of the LZ93A13 (or M60002) to pin 3 (B) of the LS139

Diagram for the connections: 

 

 For the project, the game Nobunaga's Ambition 3: Rising Sun (信長の野望・武将風雲録) was used (https://www.generation-msx.nl/software/koei/nobunagas-ambition-3-rising-sun/release/1548/):

 

 

 I put together these diagrams with pinouts in order to properly identify and solder the pins and wires:

 After, the SHARP MASK-ROM was removed and the First FLASH MEMORY was connected:

 

In order to test it, FL8.COM was used with a ROM smaller than 512 KB:

 

 

Finally, both FLASH memories were installed and tested:

 

 

And finally, it was tested as shown on this YouTube video (https://www.youtube.com/watch?v=eXTdpdrzfeM): 

In order to erase both FLASH memories, I had to change the program FL8.COM. The modified program and the source can be downloaded here (http://msxvillage.fr/upload/fl8dual.zip).

 

Also, in order to download/upload the contents of the SRAM, or even to upload 512 kB or smaller files to the first FLASH, you can use OPF version 0.78, that can be downloaded from here: https://msxcartridgeshop.com/bin/opf.zip

PS: I´ve realized that, when you connect /OE of both Flashes directly to the /RD signal of the MSX bus, the program OPF.COM recognizes the cartridge as a 1024 ASC1 FLASHROM, but you and the games lose the capability of accessing the SRAM, as both devices (FLASH and SRAM) are on the same cartridge. So, the only way to "mux" the FLASHES and the SRAM on the same cartridge is to connect /OE.00-7F to /OE of both FLASHES, as /OE of the SRAM is already connected to /OE.80-FF and as /WE of the the SRAM is already connected to /WE.80-FF of the LZ93A13. In this way, bit 7 can be used at the switching addresses of the LZ93A13 in order to select the SRAM.

 

Acknowledgements:

First, thanks to Luciano Menezes (in memoriam) for the idea of this project and for the initiative of importing some KOEI cartridges to Brazil to implement and test it.

Second, thanks to K.Tsujikawa for the diagram of the original ESE-RAM (似非RAM). どうもありがとうございます!

Finally, thanks for GDX and all the folks at the MSX Village forum (http://msxvillage.fr/forum/topic.php?id=329) for all the ideas, schematics and modifications of the original project. Merci beaucoup!