The universal 6502 RAM/ROM Expansion

This expansion was intended to give your PET or CBM computer 32kB RAM and 128kB FlashROM with many configuration options on a small board that mounts in the 6502 socket. Thanks to the use of a programmable logic chip the expansion now supports other 6502 based systems as well: currently the Commodore VIC-20 computer and many Commodore disk drives with a single 6502 CPU.

Support for other systems is possible, if their memory map is simple enough: RAM and ROM can be mapped in chunks of 2kB only.

Overview

Hardware information

Personality Chips

Overview

PET/CBM computers:

repair or diagnose computers with defective RAM and/or ROM chips.
make the computer more reliable, the expansion needs a lot less power than the original chips
expand RAM to a full 32kB
add four alternative versions of the PET system ROM
add four third party option ROMs, even in the original PET2001 that lacks the option ROM sockets
compatible with 2001-8032 series, 8296 will work as 8032 only with the expansion, 8096 and SuperPET untested.

VIC-20 computers:

repair or diagnose computers with defective RAM and/or ROM chips.
expand RAM to a full 32kB (configurable as 0kB, 3kB, 3kB+8kB and 3kB+24kB expansion)
add four alternative versions of the VIC-20 system ROM
add four internal cartridge ROM images at BLK5
fully compatible with VIC-20CR only, the VIC-20 can not be closed with the expansion

Disk drives:

repair or diagnose drives with defective RAM and/or ROM chips.
expand RAM (compatible with Maverick, RAMboard 1541/1571, DolphinDOS 2.0 1541)
add four alternative versions of the drive ROM (usually for speeder systems)
universal Flash programmer, so you can program a Flash chip for the C64 as well
compatible with all drives with a single 6502 CPU.

Building the hardware

The PCB is double sided and requires advanced skills to be built. The layout files were created with Cadsoft's Freeware version of Eagle 4.09 and can be downloaded here. The file contains layouts and schematics for other projects, too. You can also buy the PCBs from me, just visit the order page.

The following components are needed, please see the construction page for building instructions.

CN1
socket adaptor
recommended: two 20 pin SIL adaptor rows part layout

IC1
6502
you should already have this chip, it is in the
socket where you want to install this board.

IC2 1M FlashROM
or EPROM
(DIL32, 5V only, "page write")
AT29C010A recommended, also
supported are W29EE011 and W29C011A.
27C256 and 27C512 EPROMs will also
work, if you can program them.

IC3/IC3a 256k SRAM e.g. 62256 (DIL28-3, DIL28-6, SOIC)

IC4 GAL16V8 (memory decoding)

IC5 74HCT245 (bus transceiver)

IC6 74HCT157 (multiplexer for banking lines)

RP1 4.7k resistor pack (9 resistors in 10 pin package)

C1-C3
100nF capacitor

S1 DIP switch (9 switches for configuration)

IC sockets
at least one 40 pin and one 32pin socket
are needed to make space for IC5 and IC6.
Sockets for IC3 and IC4 recommended.

Personality Chips

The hardware is versatile enough to be able to work in a lot of different 6502 based computers and peripherals. With the help of a programmable logic chip the memory mapping can be set in steps of 2kB, and modes like read/write, read only, write only, or write through are possible.

So far there are personality chips for the following 6502 systems: Commodore CBM/PET, Commodore 1541/1571 disk drives, Commodore VIC-20. You can download the configuration guide and the source files for the GAL chips in the download section below.

Flash Software

Each target system needs its own version of a flash program, but there are some common points which I will describe first.

The flashmode jumper S1 will put the hardware into a state where it is possible to write to the Flash ROM, which is normally write protected. There are two levels of write protection: The hardware jumper S1, and a software write protect that is part of the Flash chip. This way the probability is very low to corrupt the contents of the Flash ROM even if the hardware write protect is disabled. Also, the option ROM jumpers S6 and S7 will get a new function: they control the bank where the ROM image is written to. This way the system can run firmware from one bank and flash another firmware into another bank.

Important note: In spite of the software write protection it is not a good idea to run the system with the flashmode enabled. This is because any write to the Flash chip will put it into a special mode where normal reading does not work anymore, which effectively makes your computer crash, if you currently run your firmware from this chip. Unfortunately some firmwares contain bugs that cause writes to the ROM, e.g. the VIC-20 KERNAL ROM and the Speeddos-ROM for the 1541. Fixed ROMs for the VIC-20 are included in the ROM archive below, see the discussion on cbm-hackers about details on the fix. A fixed Speeddos-ROM can be downloaded from d81.de.

There are flash programs for the PET and for the VIC-20, but both are still missing a user interface. Get them from the download section below. There are separate versions to flash the option ROMs and the firmware ROMs, and the images to be flashed have to be loaded to specific areas in RAM first:

PET, option ROM $9000-$AFFF: load 8kB image to $1000.
PET, firmware ROM $B000-$FFFF: load 20kB image $1000. Note that the I/O area ($E800-$EFFF) will be ignored.
VIC, option ROM $A000-$BFFF: load 8kB image to $2000.
VIC, firmware ROM $C000-$FFFF: load 16kB image to $2000.

Since the flash programs are assembled with padding bytes that fill the space to the data area, the flash programs can be easily concatenated with the raw binary data on a PC and then transferred to the target machine, e.g. with the C2N232 device. Here's an example file that takes the name of the input file and sends it to the PET:

flash.bat: (usage: flash romfile.bin)
copy /b petromflash.prg + %1 flash.prg
c2nload -c com2 -m pet flash.prg

On the PET, the PET can be put into flashmode before sending the file, on the VIC-20 (due to its ROM bug), the program must be loaded with flashmode switched off. After the program has loaded, just switch on flashmode and then issue a RUN command.

New: Marko Mäkelä wrote an improved flash program for the PET and VIC20 platforms. You can find it on Funet. Thank you very much, Marko! This program is easier to use and more powerful than mine, a very recommended download.

The flash software for disk drives is very different, I put its description to a separate page.

Downloads

Layout and schematic diagrams for all projects (Eagle format)
JEDEC and source files for the GAL personality chips
DIP switch configuration guide
Flash software for PET and VIC-20 computers
Flash software for disk drives: old version, new version

Please see the disk drive page for details.

ROM images for PET and VIC-20 computers

Currently contains both binary and program format versions of the files. The program versions will be removed as soon as the flash programs are able to load binary ROM images.
Dolphin DOS 2.0 (patched $6000 version)

This version of the Dolphin DOS 2.0 ROM for the 1541 has been patched by me to work with a RAM expansion at $6000 instead of $8000 as with the original hardware. This makes it possible to access a full 32kB of Flash ROM in the drive. The checksum bytes have been adjusted and moved to different locations. Note that this version works fine with all programs, except the original Dolphincopy that came on the utility disk. This utility has both the RAM location and parallel cable routines hardcoded. The Dolphincopy from Dolphin DOS 3.0 (with RAM at $6000) also does not work, because it doesn't have support for the old parallel cable. Important: This version needs to have RAM at $6000. It will NOT work with the standard DolphinDOS setting as described in the DIP switch settings. Make sure you configure your board correctly.

Credits

Thanks go to:

Paul Förster:
This and other PET related projects were born when Paul and I discussed options to repair his sick PET. He also gave me some good ideas in the design phase of the project. He's also my best customer :-)
Wolfgang Moser:
He's the one who helped me a lot during the test phase of the hardware, and the discussions about his Professional DOS clone project helped my project as well. Without him the nasty RAM hardware bug in disk drives would have stayed undiscovered for a very long time! Please have a look at his test report about the hardware: http://d81.de/6502RamRom/
Marko Mäkelä:
He wrote an improved flash program for the PET and VIC20 platforms. You can find it on Funet. Thank you very much, Marko!
Michael Sachse:
He wrote a menu driven Flash program for the CBM series!
Homepage: http://www.cbmhardware.de/cbmpet/romram.php
Discussion board with new versions (registration needed): http://www.forum-64.de/wbb2/thread.php?threadid=9746
Tim Schürmann:
He also tested my hardware and wrote a test report about using my hardware as a Dolphin DOS replacement (German language only). Have a look at his page here: http://www.tim-schuermann.de/c64/de/index.html
and everyone else who bought hardware from me and supported the project this way!

Contact

If you have questions about this project, you can mail me: please visit my contact page.

CN1	socket adaptor	recommended: two 20 pin SIL adaptor rows
IC1	6502	you should already have this chip, it is in the socket where you want to install this board.
IC2	1M FlashROM or EPROM	(DIL32, 5V only, "page write") AT29C010A recommended, also supported are W29EE011 and W29C011A. 27C256 and 27C512 EPROMs will also work, if you can program them.
IC3/IC3a	256k SRAM	e.g. 62256 (DIL28-3, DIL28-6, SOIC)
IC4	GAL16V8	(memory decoding)
IC5	74HCT245	(bus transceiver)
IC6	74HCT157	(multiplexer for banking lines)
RP1	4.7k resistor pack	(9 resistors in 10 pin package)
C1-C3	100nF capacitor
S1	DIP switch	(9 switches for configuration)
	IC sockets	at least one 40 pin and one 32pin socket are needed to make space for IC5 and IC6. Sockets for IC3 and IC4 recommended.

The universal 6502 RAM/ROM Expansion

Contents

Overview

Building the hardware

Personality Chips

Flash Software

Downloads

Credits

Contact