I used my CNC to isolation-route the design. I’ve provided the PCB layout in case you have the ability to etch your own PCBs. Instead, I chose to make the PCB design as simple as possible (so I could etch it with my CNC) and then deal with the complexity in software.ĭesigned from the component side – looking down on it from above. Speed isn’t particularly an issue when programming parallel EEPROMs, so I didn’t feel any real need to control the digital pins at the port level (an optimisation which would allow us to control eight bits in one go, rather than each bit at a time). The circuit is just an iteration on my post about reading parallel ROMs … but now it writes, too. I’ve also added red and green LEDs so I get visual feedback when it is reading or writing.

It just sits on top of the IO pins on the far end of the Mega, and routes those pins to a ZIF socket. However, when I started looking at the small extra cost of an Arduino Mega (with all its many digital I/O pins) I realised that I could make just as simple a programmer (with NO extra components) in a much shorter time.įor a while I would just put a EEPROM programmer together with a Mega, a breadboard and a lot of jumper wires whenever I needed it, but that got annoying really quickly! And there was always the worry that one of the many wires could be loose, and the EEPROM programmed incorrectly. My initial design for a programmer involved an Arduino Nano and some 74xx595s for the address lines … in fact, when I discovered this site later on, I was pleasantly surprised to see someone else’s design use exactly the same approach.

So: I need a small, not particularly powerful computer, but with a good amount of digital I/O pins. If I had the space to setup my RiscPC I might have been tempted to program it via its parallel printer port … but I don’t really have the space, and I’d ideally like the programmer to be small, that I can leave in a box when I don’t need it. Programming a parallel EEPROM is nice and logical and straightforward, and can be done with very few components. There’s no blanking-under-UV process, no special programming voltage required … I always feel like EEPROMs behave how you’d expect a programmable, read-only memory component to behave. I like EEPROMs, certainly compared to EPROMs. I’ve been experimenting with BBC micros, and building my own DIY-6502 single-board computer. There’s been a number of occasions recently where I’ve needed to program a parallel EEPROM. I should be documenting before I start on the next one.Īnyway, here’s one that’s been half-written-up for a while, that’s nice and self-contained. Which is a poor habit to get into, I admit. I’ve had so many projects on, but I’ve not been able to spend a serious amount of time documenting them.

Not posted in a while, have I? It’s not because I haven’t been tinkering – actually, it’s the reverse.

27c256 eprom programmer