6502.org

Hi.

I had needed a EPROM emulator instead of using a burner and move chips back and forth all the time. I have googled a little but it seems like there are no one that makes any anymore (everything I found was old and not available). It was also very expensive. Around $500. Are there any relative cheap ones?

If you can't get one second hand you will have to build your own. Or you use a completely different approach and use a microcontroller to load the ROM image into a RAM section that can be write protected. Either you use the blind load method or you use BE. This also allows for higher clock rates. I used the blind load method in my ROMulus viewtopic.php?f=4&t=3458&hilit=blind+load+romulus. Images can be loaded from AVR flash or Xmodem.

Cheapest, No development approach would be using EEPROMs I think.

You need some headers, a pin compatible EEPROM, a ZIF socket and a EPROM programmer. (Like TL866CS)

1. Wire headers and zif socket's pins
2. Put the headers on the IC socket where normally EPROM would be placed.
3. Program EEPROM
4. Place it on the ZIF socket

To change content of the EEPROM just remove it from the ZIF socket and reprogram it and place it again on the ZIF socket.

To add to i_r_on's post, I would comment that my (E)EPROM programmer, using the quick programming algorithms, can program an 8KB EPROM just about as fast as you can put it in the ZIF and get it back out. A ROM emulator might take the same couple of seconds to transfer the image. My Needham's EPROM programmer is in a PC card slot, so transfer is not a separate process; although I would like to get a stand-alone programmer too which would not be tied to any particular hardware or software or OS. I used one years ago, a Bytek Writer, which had a keypad which could be used for data entry/editing and for giving it instructions, but could also take all the in from RS-232. I even used my HP handheld computer to control it in the 1980's.

Yes this is what I have been doing in the past. Also used battery backuped SRAM and it works, but it had been much more convenient not to need move the chip around all the time. I can build something for it, but I hate creating a project just to be able to start the real project.

Did you see this project? https://hackaday.io/project/8109-sram-a ... -for-eprom

===Jac

I have used SRAM with builtin batteries in the past. Maybe more expensive than his solution but the same function. You still need to move it between the programmer and the project. I had liked to just have a cable attached and be able to program several kb in a few seconds.

Could you use a battery backed, dual port ram, with one "side" configured for the programmer, the other with a flying lead with a header for the board ??

I don't think there are any dual port memories that would work. It should be something that has the same pinout as a 27c64 for example.

You might also want to look at my L-Star project which uses a Propeller to bitbang a 65C02 and make it "think" that it's in another computer such as an Apple-1 or an OSI Superboard. I used it as a RAM/ROM emulator to repair my MicroKIM, simply by modifying the Propeller firmware a little and plugging it into the MicroKim expansion port.

I'd be happy to help you design a circuit board that can be plugged into a ROM socket, with just a Propeller (and crystal, capacitors and 24LC256 EEPROM), and adapt the software so that it emulates whatever EPROM or ROM you want to replace, up to 32KB. The Propeller is programmed through a serial port (usually via a USB converter) and programming can be done "semi-live" i.e. it can stay plugged into the circuit under test while you program it, but of course during programming it won't emulate, so you have to turn the circuit under test off, or at least reset it while programming. Programming takes a few seconds depending on the size of the ROM.

===Jac

What clock speed are you using in your system, respectively what is the access time required by the "ROM"? When you have a moderate clock you can just use a cable from the EPROM socket to the ROM emulator. Then your solution does not need to fit into the socket space completely.

Howdy...

There are some really interesting projects with the Propeller.
I recently tried to read the Address and Data bus of my W65C816SXB board with a propeller.
The propeller was not able to read it due to the fact that it runs @ 8MHz and my propeller only had a few cycles to read the data bus.
Seem like it's doable with both read and write at around 1MHz ?

I need to check out this projects in more detail when I have some time...

SoftTec has a great EPROM emulator, but it's LPT driven