ET-3400 ROM - Programming Adaptor

Thinking that it would be far more convenient to have a programming adaptor to program the SMD EEPROM after it was installed, rather than once off before it was installed I kept worrying had I allowed adequate space to design one at a later stage after this project was completed.

I thought that with a bit of time up my sleeve before the end of the RetroChallenge I'd like to be sure that it was do-able and that I wasn't going to make something that was difficult or impossible to reprogram.

I decided to start a PCB layout for a programming adaptor just to see if it was going to work. That was 2 days ago, and I realised that one of the pads that I had for the extra 4 pins was not in the best location, so I decided to spend some time in moving the pad to make the design of the adaptor workable.

At first I was only going to do part of the layout, but once I got into it the retro adrenaline kicked in and I could see that it wasn't too difficult to finish it off. So now I have virtually completed the Programming Adaptor as well. Since I have never used pogo pins and I don't have any at all I will still leave the final Programming Adaptor until a later time when I work out exactly what type and size I need. For now I will assume that a pogo pin that is 75mil dia at the base and needs a 32mil hole in the PCB will do the job. That was one of the specs I looked up.

The two centre strips of pins plug into the programmer, while the outside edge pins are for the ROM replacement board to plug into. The 4 larger pads in the middle are for the pogo pins for the extra signals.

This is the draft version of the adaptor layout. I need to do a 100% check on this one too as it's quite confusing working on ICs that are rotated 180 degrees to the PCB orientation in the programmer. I also wanted to make sure the adaptor would work in the TL866 Plus which a lot of people seem to have, and they align the IC to the top of the socket. Mine is aligned at the bottom of the socket, but it works there as well.

This additional task has delayed my final gerber files for the ET-3400 ROM adaptor by a couple of days, but I should have those completed sometime tomorrow... 


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