HCR Micron Plus EPROM Programmer

[hoglet]

Hi all,

I'm interested in the HCR Micron Plus EPROM Programmer, as this seems to be one of the best of the original BBC Micro EPROM programmers.

It connects to the 1MHz bus and has on-board memory to allow it to deal with larger (32KB/64KB/128KB) devices. It supports programming voltages of 25V, 21V and 12.5V, and will even program the Atom 2532 EPROMs.

The manual is here [retrokit] and there is good video of it here [Least Significant Byte].

I'm not aware of any reviews.

I was actually considering reverse engineering this programmer and trying to build a replica. Unfortunately I don't have an original device, and they don't come up on eBay very often.

Does anyone know if the schematic exists anywhere?

I was also wondering if someone with one of these devices would be prepared to take some good internal photos that might facilitate reverse engineering the design.

regards

Dave

[Mince]

I have a working one of these - I’ll try and take some photos this evening.

I tend to use it rarely these days as I moved from a GoSDC to a Pi1MHz and it’s a faff to remove the Pi1MHz, and I have one of those TL866 programmers that seems to do the same job.

[hoglet]

I have a working one of these - I’ll try and take some photos this evening.

That would be great - I couldn't find any photos of the insides anywhere.

I tend to use it rarely these days as I moved from a GoSSC to a Pi1MHz and it’s a faff to remove the Pi1MHz, and I have one of those TL866 programmers that seems to do the same job.

I think the older TL866 models are actually better than the TL866II Plus, which only supports Vpp of 18V max. The current model, the T48, might better though.

I have always struggled to program 21V and 25V EPROMs with modern USB-connected programmers, as they can't draw enough current from the USB 5V supply.

Back in the day I built my own programmer, see:
- Hoglet's Past Projects #3 - the EPROM Programmer
Writing the software for this was great fun. It works fine, but only supports 21V 2764/27128 parts.

The HCR Micron Plus seems like a nice middle ground, and it would be fun to try to rebuild this in 2023. I think if PCBs were available, this might be quite a popular project.

Dave

[Mince]

Here you go... it's a right sod to get the board unscrewed from the top cover because of the lips on the case and the way they've used a bolt and three nuts to hold it in!

The chip hidden under the power cord is the same as the one above it.

Let me know if you need anything else before I screw it back together!

[hoglet]

Let me know if you need anything else before I screw it back together!

Thanks, that's very helpful.

There's quite a lot in there, isn't there?

What's the number on the TTL chip to the left of the transformer?

Can you read any of the markings on the transistors and/or regulators and/or electrolytic capacitors?

Dave

[Mince]

Sorry — I realised after I took this, I could have taken a better shot of the board, after I removed it from the lid:

The IC to the left of the transformer is SN74LS138N.

The regulator diagonally mounted next to the purple capacitors is LM 317SP 8621. The transistor near that looks like 624 LM317 LZ.

The small purple capacitor is 100µF 16V; the large one 2200µF 16V. The little blue one looks like 200µF (labelled 220MFD), 16VDC; the larger blue ones 220µF 63V.

Sorry — phpBB doesn't seem to have honoured the rotating information!

Let me know if you want any more or if I've missed something!

[hoglet]

Let me know if you want any more or if I've missed something!

Last question: can you read the markings on any of the three smaller transistors in the power supply area?

I'll work on these tomorrow and see if I can start sketching out a schematic.

Dave

[Mince]

Which are the smaller transistors? I can see two large-ish silver can transistors, one of which has 2N2905A 7541 on it; the other looks the have the same thing written on it (I can't see the A, but everything else is the same).

Sorry if I'm not recognising the components correctly! If I've missed anything else, you might be best circling it on a diagram!

What's the black thing with W005 written on it, BTW?

As an aside, there's a sticky label on the bottom with "24.7.86" handwritten on it, so I assume that's the date of manufacture!

[hoglet]

Sorry if I'm not recognising the components correctly! If I've missed anything else, you might be best circling it on a diagram!

The other device I thought was a transistor is, on closer inspection, another LM317 in a TO92 package. So that's them all covered.

What's the black thing with W005 written on it, BTW?

It's a 50V 1.5A bridge rectifier.

As an aside, there's a sticky label on the bottom with "24.7.86" handwritten on it, so I assume that's the date of manufacture!

That sounds about right.

That's given me lots to be getting on with! Thanks.

Dave

[Mince]

The other device I thought was a transistor is, on closer inspection, another LM317 in a TO92 package. So that's them all covered.

Ah, I thought you might have meant that. That was the one I mentioned earlier which I thought was a transistor too, until I Googled LM317 and noticed that was also on the more obvious regulator-looking regulator near the heatsink! That made me think you were talking about something else.

What's the black thing with W005 written on it, BTW?

It's a 50V 1.5A bridge rectifier.

Ah, I thought it would have been, given the two AC symbols and + written on it. I was just expecting to see a -ve somewhere, but I know very little about electronics!

I'll screw it back together as I keep getting worried I'm going to knock it on the floor but I can look some more if you have further questions.

[KenLowe]

I tend to use it rarely these days as I moved from a GoSDC to a Pi1MHz and it’s a faff to remove the Pi1MHz

If using one of my Pi1MHz level shifter boards, it previously wasn't possible to have a second device attached to the 1MHz bus at the same time due to bus conflicts. However, with a minor modification to the level shifter, and an update to the Pi1MHz firmware it should now be possible to have both devices attached at the same time:

viewtopic.php?t=27717

Obviously, this only works if you're using a ribbon cable that has multiple IDC headers for attaching more than one device to the 1MHz bus. If you've got the Pi1MHz level shifter plugged directly into the 1MHz connector on the underside of the keyboard then you'll have no physical way to attach a second device.

[Mince]

Thanks — I did see the thread and had recently updated all my Pi1MHzs to the new software: not that I have done the mods, or have multiple devices, but just to get everything onto the latest version. I wasn't particularly thinking how it might be useful to me, though, so I'll read the thread in more detail!

[BeebMaster]

There is a lot inside there, isn't there! Especially when compared to the Morley one. And it's pretty unusual I think connecting to the 1MHz bus rather than the user port.

I'd definitely be interested in an additional EPROM programmer, I am worried that if my Morley one breaks down, I would have to fall back to my SC84 which I've only ever used to duplicate EPROMs, and not program any (via serial). The Morley one does do 21V as well as 12V but I haven't programmed a 21V device for many years. The 27C256 EPROMs I stocked up on in quantity 20 years ago are 12.5/12.75V. The maximum size it will do is 27256, in "high" and "low" halves, and I don't think it will do 24-pin devices.

I do have a couple of tubes of 2732 (and 2764), I will have to check the programming voltage they need.

[BeebMaster]

Oh. Apparently I don't have any 2764 at all, and only 5 2732A (marked 21V FAST) mixed up in a tube with 9 2716 with no voltage given. Also I have a tube of 27C16 all date coded 0036, which sounds positively modern, marked as 12.75V. Plus I have in storage "Box of ROMS/EPROMS, various inc 2532 24-pin", but these are not further catalogued so I don't know what they are.

[Mince]

I understand the HCR one is pretty rapid compared to others but I’ve only used this one (aside from my TL866II+), so don’t have anything to compare it to — it writes a 27128 in about two minutes.

I’ve written 27256s in one go, I think, but I’m not clear where the software stores it all in memory. I’ve written a 27513 but I think I did that in stages.

[hoglet]

I’ve written 27256s in one go, I think, but I’m not clear where the software stores it all in memory. I’ve written a 27513 but I think I did that in stages.

It stores the first 16KB in main memory from 0x2000 to 0x5FFF and then the second 16KB in RAM on the programmer (using two 6264 8KBx8 devices).

I've made some progress with the reverse engineering today, but it's slow going and involves a lot of guess work, especially with the traces on the component side.

I've also been doing a disassembly, which has helped clarify some things.

Mince, if I get completely stuck, I might ask you to take a bunch more photos of the component side from slightly different angles. Also, it might help to have the original photos, as the forum has shrunk them down quite a bit.

Dave

[Mince]

Thanks for the explanation — it's interesting it has all that RAM on the programmer. That is hidden from you, when you use the software.

I've uploaded all the photos I took (including some duplicates of the same thing, and some I didn't upload) here: https://www.dropbox.com/scl/fo/w2cdxkwp ... ske34&dl=0

Let me know if you want any more. I might trade you for a spot of help on why my PiDP-11 is running like a tortoise (which seems to have been caused by me adding a serial interface), although I don't think you owe me anything!

[hoglet]

I've uploaded all the photos I took (including some duplicates of the same thing, and some I didn't upload) here: https://www.dropbox.com/scl/fo/w2cdxkwp ... ske34&dl=0

Thanks, those will get me a bit further.

Let me know if you want any more. I might trade you for a spot of help on why my PiDP-11 is running like a tortoise (which seems to have been caused by me adding a serial interface), although I don't think you owe me anything!

Does this sound like what you are seeing:
https://groups.google.com/g/pidp-11/c/m ... -nKG80AgAJ

Dave

[Mince]

Thanks — the issue I'm seeing is the Pi itself slowing down massively (things like 'apt upgrade' can take over an hour, and everything's very sluggish), and report that the voltage is dropping. This makes me think I've done something wrong with the modification, like getting the components choice wrong (there are a lot of different MAX232 variants, for example!).

I posted a full description here (to avoid clogging up this thread!): https://groups.google.com/g/pidp-11/c/Q ... tPglVsAgAJ

[hoglet]

I posted a full description here (to avoid clogging up this thread!): https://groups.google.com/g/pidp-11/c/Q ... tPglVsAgAJ

Any chance you could start a thread on here and post a photo or two?

In PiTubeDirect we found if the Pi's UART is enabled without configuring weak pullups on GPIO 14/15 then the UART RxD line will float low. In this state the UART sees an endless stream of Null characters. This is a bit surprising, because UARTs normally identify the start bit with a 1->0 transition. So it appears the Pi UART works differenty. This caused all manner of issues with PiTubeDirect, as the UART interrupt handler was running every 100us. I'm not sure if all Pi models work like this, or just the ones that use the BCM2835.

So, it might be worth checking with a scope that the UART RxD pin on the Pi GPIO connector is close to 3.3V in the idle state, when no characters are being transmitted.

In fact, this page suggests the Pidp-11 has a voltage divider on the RxD pin. If nothing is connected, this will infact be pulling it low, even if a weak pullup is enabled.

Dave

[hoglet]

Back onto the EPROM programmer...

Mince, a couple more questions:

1. With the programmer plugged in and switched on, could you run the following:

Code: Select all

10 MODE 3
20 @%=5
30 FOR A=0 TO 255
40 PRINT ~A?&FC00;
50 NEXT

I'm expecting the programmer to show up at &FCC0-&FCC7 (the 4th line from the bottom), but it's possible it will alias as well.

2. When using the programmer, are you able to hear the relays click?

Do they only click on device selection, or do they also click during programming?

Dave

[Pernod]

I'm expecting the programmer to show up at &FCC0-&FCC7 (the 4th line from the bottom), but it's possible it will alias as well.

Agreed, the two PIA's are at C0-C3, C4-C7.

I haven't noticed any writes to JIM for the RAM, so suspect that's also accessed via the PIA's.

[Mince]

1. With the programmer plugged in and switched on, could you run the following:
...
I'm expecting the programmer to show up at &FCC0-&FCC7 (the 4th line from the bottom), but it's possible it will alias as well.

Yes — all FF except for the first 8 on the fourth line up from the bottom.

2. When using the programmer, are you able to hear the relays click?

Do they only click on device selection, or do they also click during programming?

They seem to only click when programming particular sizes of EPROM and click back after programming (although I don't actually have a chip in there for most: it clicks, fails and clicks back). The 27256, 27128, 2764 and 27011 don't involve any clicking; 27513, 27512, 2732, 2716, 2564 and 2532 do (I'm guessing that corresponds to pinout changes).

The clicking isn't affected by selecting different programming voltages.

[hoglet]

I found an advert in Acorn User December 1987 (p202) for the Micron Plus 128K:

Dave

[Mince]

I've seen SWROMs version 1.30 and 1.40 and the latter is described as "128K" (although that may have been just a filename suffix).

I'm not sure which one I have: certainly it will program the 128K ROMs but it asks me which bank (0-3), so they would be 32K in size. That might imply more memory in the programmer, except it says that 128K ones are Master only. I use the 1.40 software with it.

[hoglet]

Hi all,

I've finally captured what I hope is an accurate schematic of the Issue 1 Micron Plus EPROM programmer:

micron_plus.pdf

(427.26 KiB) Downloaded 40 times

The KiCAD files are in github:
https://github.com/hoglet67/HCRMicronPlus/tree/original

It mostly makes sense, but there was a lot of guess work involved working just from photos, so it's possible there might be some errors. The power supply section is interesting, particularly the use of a polarized capacitor directly in series with the transformer secondary! I think this is being used to boost double the voltage of the 9VAC secondary (i.e. it's a one stage diode/capacitor voltage multiplier). But I haven't ever seen this done before in this type of power supply, so I would be interested in other peoples thoughts. If it is a voltage multipler, then the capacitor is fitted backwards!

Here's a PDF of just that page:

micron_plus-Power Supply.pdf

(79.63 KiB) Downloaded 24 times

I've also checked in what I have so far on the ROM Disassembly (version 1.41)
https://github.com/hoglet67/HCRMicronPl ... HCR141.asm

I really would like to try to reproduce the PCB for this. But I'm not sure how faithfully to follow the original. It will be hard to source a transformer with 6V and 9V secondaries. It might be better to redesign the power supply section to run off an external 9V power supply brick and use a modern boost regulator to generate the 28V supply needed for VPP. Something like this:

Next steps are to do a bit more work on the disassembly, and see if it appears consistent with the schematic.

Also, Wookie is sending me some photos of an Issue 2 board, so it will be interesting to see if there are any changes other than fixing the bodge wires on the Issue 1.

Dave

[vanekp]

wow amazing work, use to use one of them at my work in the 80's it was a very nice programmer and worked very well.

[lushprojects]

It mostly makes sense, but there was a lot of guess work involved working just from photos, so it's possible there might be some errors. The power supply section is interesting, particularly the use of a polarized capacitor directly in series with the transformer secondary!

If this sim is right then provided the peak voltage from the secondary is less than the DC voltage from the supply it's bootstrapped from the polarity of the capacitor is correct.
https://tinyurl.com/yqxs6xy4

[hoglet]

If this sim is right then provided the peak voltage from the secondary is less than the DC voltage from the supply it's bootstrapped from the polarity of the capacitor is correct.
https://tinyurl.com/yqxs6xy4

That's really helpful, but something isn't right here.

I've rechecked the circuit and I got the connection to the first diode wrong; it connects back to the transformer secondary.

So the circuit looks more like this
https://tinyurl.com/yut2qv47

And the capacitor does need to be reversed.

I'll update the schematic tomorrow.

Interestly, looking at photos of the Issue 2 from Wookie, on his board the capacitor is actually reversed!

Dave

[1024MAK]

I’m curious, how did you decide that the transformer secondary for the 5V regulator is 6V?

Assuming the transformer regulation is perfect (it won’t be), the best case scenario is that the peak AC voltage is 1.414 X the RMS AC voltage, so with a 6V secondary, that’s 8.49V

Then you need to deduct the forward voltage of the bridge rectifier, which is two silicon junctions. Best case is that’s 2 X 0.7V.

So 8.49V - 1.4V = 7.09V

Under load however, the effective peak voltage will be lower. And the forward voltage of the bridge rectifier will be higher. Hence the voltage to the 7805 will be lower. When taking the ripple voltage into account, that’s a bit low unless the load current is very low.

Is it possible that the transformer has two 9V secondaries? An off the shelf transformer would have been cheaper and easier than a custom wound transformer.

Mark