The (not only) CPU board

A project log for MRC6502 - Modular Retro Computer

MRC6502 is a fantastic opportunity to learn more about digital electronics and 6502 assembly programming... step by step.

padnestpadnest 01/28/2022 at 14:480 Comments

The CPU board hosts:

In this board prototype I forgot to add a jumper in order to manually select the ROM banking (RAM14).

I will add another jumper for this scope in the next revision.

Schematics: here

CPU (1)

The CPU is the WDC W65c02s processor and it has many improvements against the old MOS 6502:

Datasheet: here

RAM (2)

64Kb of static RAM are provided by two HM62256LP-70.

Datasheet: here

ROM (3)

A ZIF socket to host the 32Kb AT28C256 EEPROM.

Datasheet: here

PLD (4)

All the system 'glue logic' is managed by an ATmel ATF22V10C-15.

Datasheet: here

Memory configuration (5)

The jumpers can be used to control what to read at address ranges A000-BFFF (EROM1) and E000-FFFF (EROM2).

You can exclude and override the respective EROMx signals generated by one of the VIA (that can be programmatically used to control the configuration).