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Burning 16-bit EPROMs with a Willem Programmer

This wasn't fun! I wanted to get Kickstart 1.3 on my Amiga 500 and so I purchased some M27C400 EPROMs from eBay with the thought that I could host two ROMs on them and make it switchable. The ROMs arrived and, to my stupidity, didn't fit in a standard Willem EPROM Programmer! Of course, a quick google prior to purchasing anything would've made this very apparent. Fortunately, there's a fix! You can buy a DIP42 16-bit EPROM Adapter for the Willem, and so I did.

Thanks to COVID, it took an extra-specially long time to arrive and, once it did, got thrown into the box'o'Amiga'junk as I'd put the whole lot on the backburner whilst working on the Ataris of late. This weekend I'd finally managed to wrangle some time together and sat down with my trusty XP laptop to program these chips.... It wasn't easy!

Input Voltages

I jumped head-first into the programming and failed a LOT with errors such as 0x00 and 0x11. Any search online will tell you that, when getting lots of 0x00 and 0x11 errors, it mainly indicates that you aren't supplying the correct programming voltage for your target chip. Check out the PDF Datasheet for the chip you want to burn, it'll specify a programming voltage that it requires to successfully understand and store the bits that you're about to throw at it.

For the M27C400, we need to provide 12.5v +/- 0.25v. The Willem has a blue trimmable capacitor (or is that a resistor) on the top-right of the board that you can adjust to get this voltage. I always recommend to use an external power supply with these programmers and so I have a plug-pack which happily provides 12v @ 2amps. To make sure we'll have a chance of programming this chip, switch to the Test H/W tab of the software and tick VPP. This is pin 1 of the E32 socket. If this has worked, then you'll have a red LED illuminated on the board. Now, check the voltage between pin 16 (GND) and pin 1 (VPP) of the socket.

Mine was reporting a value lower than 12v to start with and hence I had a few issues burning. With a multimeter in place, I tuned the trimmer on the top-right and got the value to 12.5v. Actually, it was probably 12.6... but 12.4 would also work as you just need to be in the range of 12.25 - 12.75.

Another test burn saw a new error... no more 0x00 and 0x11, it was now further into the chip, usually around 0x100?

Willem Software vs. Programmer Settings

Next up, we need to make sure that you can correctly control ALL address lines with your Willem Programmer. After fixing the initial errors above, I started getting new errors at random intervals into the burning process. The errors all seemed to indicate that there was an issue writing data after address 0x100. I'd only been using empty chips, so it couldn't be because they already had data on them. You can also check if the chips are empty prior to burning and I totally recommend doing this. Either way, after this new error was received, I chose to then read the chips and view the data:

What you're seeing above is the data read back from the chip. I wrote the rom (loaded from file) to the chip, got the error and then chose to read the data from the chip back into the application. 75% of the data on that screen is correct, but you'll notice that the data repeats itself from 0x100! It turns out that this was all due to the fact that my Willem was only controlling the first 8 address lines and leaving the rest low. I recommend you rig up an LED test harness as per below and control the address pins via the Test H/W tab on the Willem Software.

After swapping chips around, checking continuity between the 4051s and reseating everything else, I came to the conclusion that there's incorrect information in the Standard Willem Programming Guide. If you scroll to page 5, you'll find information on the version of the software to use. It suggests that, based on jumper settings on the board, you can select if the board emulates a PCB3B or PCB3.5. If you've chosen PCB3B, then you'll need to use software version 0.97ja, as per my post from a long time ago, when I was failing with the same issue! Alternatively, if you've chosen PCB3.5, you need to use 0.98d6 or higher.

I looked at my board and checked out the jumpers that set the board emulation. Mine were actually individually set to 1-2 and 2-3 instead of both 1-2 or both 2-3. Hah... how did this thing ever work?! With these jumpers now set to 2-3 (aka PCB3B), I went back to version 0.97ja of the software and tried to get the full suite of address lines to light up via the Test H/W tab. No dice! If you browse to page 6 of the above PDF, you'll find that the jumpers should be set to 1-2 for PCB35 and 2-3 for PCB3B. Just for fun, I switched the jumpers to 1-2 and tested out version 0.98d6 of the burning software... still no dice! No permutation of checkboxes on the Test H/W tab would get a high signal on any of the address lines higher than A7! Up until this point in time, I'd only programmed 8-bit EPROMs, so I'd never noticed this.

I went ahead and played musical-chips. There's a chain of CD4015BE ICs that shift out the address lines, 3 of them with 1 each controlling 8 bits. It seemed plausible that there might have been a faulty connection between the first and second, but no amount of tinkering brought the address pins to life. I took a break as the frustration (or was that sadness) levels were elevating and sat down to a bit of TV. With a fresh mindset, I came back to the device, forgetting which settings were applied. Opening up version 0.97ja and testing address lines now worked!? Wait, the jumpers are set for PCB35... what the hell, it's backwards!? I opened 0.98d6 and it didn't work, so I set the jumpers back to 2-3 (for PCB3B) and it now 0.98d6 worked!? Urgh... so much time lost. So, TLDR; The PCB3B/PCB35 jumper settings are backwards on my Willem Programmer. Set them to 1-2 for PCB3B and 2-3 for PCB35!

Using the adapter

First up, there's two jumpers on the adapter to configure. The right-most controls the VPP/A21 line and needs to be set to 1-2 for M27C400 or M27C800 EPROMs. The other, in the middle of the board, I left at 1-2 as I don't know what it does.

Next up, there's a ribbon cable used to obtain more address pins from the main programming board. For the M27C400, the base E32 socket of the Willem actually produces enough address lines, so this ribbon cable isn't actually needed. Check out the diagram below to work out how the adapter is constructed. I've coloured the lines that are used on the M27C400 and 800, where you can see that the 400 doesn't use any of the wires from the header on the right.

If you're going to program an M27C800 or larger, you'll need to connect this. Simply make sure that pin A23 (bottom-most) lines up with A23 on the Willem board.

Finally, when inserting ANY chip into to the socket, make sure that the pins are all straight and that none will foul. For any of the chips, always make sure that the bottom pins are at the bottom end of the socket. The EPROMs are designed so that the Address lines extend 'north', so the silhouette on the board is actually for an M27C800. An M27C400 will be one pin lower than the silhouette, aligned at the bottom of the socket.

Conclusion

All the errors I made above would've been avoided if I'd known what I was doing from the start. Usually the old RTFM instruction makes sense, but when the jumper settings work in reverse to the manual, it's a little frustrating. On another note, I'd just trusted that this piece of hardware worked, as I've managed to burn other chips in the past. Assuming that cheap hardware just-works(tm) is a flaw in itself. Always make sure you know the hardware you're working with back-to-front, which was totally possible this time around thanks to open-source schematics being available!