Yet another manual programmer for old fuse PROM chips

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Nothing fancy here, just a circuit to burn some 74188/K155RE3/DM8223N because this is not supported by most universal programmers.
This is really in the retro category because these chips appeared in the early 70s before PAL/PLDs were a thing and they are pretty easy to program by hand, without crazy algorithms... once you figure it out !
I thought about making it with a Pi but wiring it would be faster and I didn't want to spend time with software... Not yet, since I don't have many to burn.

Oh, you ask why I would bother ? Because 7 segments decoders are often limited to BCD and it's pretty cool to have arbitrary 5-inputs logic with no software and the accompanying obsolescence. It could be handy for hassle-free address decoding as well.

I'll see if I can later adapt the circuit for the 256×4 PROM (74187/K155RE23) for other purposes.

1. References
2. First casualties
3. Design considerations

Decoding hexadecimal to 7 segments has been a long story, that has been brought back to life with the #Discrete YASEP and gave life to the #PICTIL and #DYPLED ... but it was still not satisfying because they are really modern.

Hexadecimal decoding chips are not easy to find but a smart guy solved this :

Numitron replacement of TIL311

I had been interested in Numitron displays lately and this one gave me a critical hint with one of the pictures:

The decoding chip is actually a PROM : the K155RE3 is a Russian equivalent of the SN74188. Each segment draws up to 20mA but can work at a slightly lower current, so this is close to the circuit's limit but still manageable.

The 5 address lines are enough for a hexadecimal decoder. The extra line could be used for "reverse polarity", as hinted by the jumper labelled by the silk screen "Non-Inv". Another use would be a backup area if the first half contains an error (errare humanum est). No idea how the 8th data bit can be used though.

I could find some of these parts AND information about the programming procedure, thanks to several people who did it as well !

One awesome advantage of having custom decoder chips is the ability to extend the "vocabulary" as well as remapping the pins to ease routing of the PCB traces.

Small and fast PROMs are useful for quite a few other purposes, such as small FSM, address decoding, translation of register number (in the #YGRECmos ), so having my own burner is pretty handy. I have a number of PAL22V10 but they are often overkill and it's not easy to generate the JEDEC programming files... My MiniPRO TL866A can flash the PAL but without a JEDEC file, they are quite useless.


  • Design considerations

    Yann Guidon / YGDES07/16/2017 at 21:30 0 comments

    (moved from the project description page)

    Since I want to program both 74187 and 74188, I need 8 bits of input and 8 bits of output. I started with my favourite parts: a couple of hexadecimal encoding wheels and a couple of TIL311 for the address bus.

    The data bus is a bit unusual : one of the data bits is shorted to 0V, so I use a 11-positions rotary switch (leftover from the #Clockwork germanium discrete clock project) to select the desired bit. For the lower nibble (in the 74187 case) I might add a TIL311 for inspection of the output but LEDs should be enough otherwise. A 7-segments module is used as well to check the output.

    The fuse is blown when the power supply is raised from 5V to 10.5V. The different voltage sources are isolated by diodes so approximately 5.6V and 11.2V are required. Add to this that the TIL311 are undervolted at 3.6V... That's a few diode drops, but too close to the margins to use LM317s.

    Starting from 12V, two diode drops provide about 10.6V but this is not accurately regulated and might affect the programming. A 14 or 15V input source would allow the use of a LM317 so the power supply would be a 12V unregulated "wall wart" (let's see what I have in stock).

    From 10.6V down to 5.6V, another LM317 drops 5V. This is probably the one that dissipates the most power.

    Then from 5.6V to 3.6V, two volts are dropped but the TIL311 power rail does not need a tight regulation so a string of 3 silicon diodes would do.

    The TIL311's current is measured in the 125mA ballpark (around 60mA per module) and this is the most consuming circuit. The power drops are: 1/4W for the 2V drop and 0.7W for the 5V drop. This is significant but still in the range of the circuits made in the 80s... The good side is : this current keeps the LM317 in the regulation range. In the end, the wall wart must provide at least 200mA (probably rated at 500mA) and most of it will be turned into heat.

    I found several LT1086, in fixed and adjustable versions, with are low dropout versions.

    Minimum load current less than 5mA, input voltage is high enough (25V max) and the dropout does not exceed 1.5V at max current. That's just enough margin for the input regulator (11V) and the TIL311 rail (5.6V to 3.6V) without weird hacks.

    Let's start with the 3.6V rail : I got the regulator and I just have to add a couple of resistors to set the voltage. I find that the ratio of resistors is 2.88 so if I set one resistor to 1K Ohms, all I have to do is find a 2.88K-1K=1.9K resistor. Fortunately this is close to the standard 1.8K value, and the voltage does not need high precision. There is also a need of capacitors but that's not a critical consideration... 100uF/25V will do, I have a significant number of them in stock. Ahem.

    The 1.8K and 1K resistors give about 3.59V which is pretty good :-)

    This works quite well when you don't mistake a fixed with an adjustable version. And it also made me devise a little trick to calculate the resistors : just convert the volts in kiloohms :-) With a 1.2K resistor for the adjust pin, if I want 3.6V I need 3600-1200=2400 ohms. This is less reliable because of the disturbance of the adjust pin's current but we'll add a trimpot later.

    For the 5.6V part I'll use a different trick that the datasheet suggests:

    If we consider that 1K provides a 5V swing, 1K/5=200 ohms will provide the required 1V swing :-) That's possible though if I haven't burned the first LT1086-5 that I mistook for an adjustable version for my first attempt...

    (Now I realise I could have used this trick because I have 3.3V versions and that would have saved one resistor)

    With a 330 Ohms trimpot, I can vary the output from 5V to 6.8V :-) This amounts to about 180 ohms per Volt so a 1K resistor will increase the output by about 5.4V, resulting in 10.4V.

    Using a 990 Ohms and the same type of 330 Ohm trimpot, I get a range of 9.6V to 11.2V, which is perfect. The 10.5V output is obtained with the trimmer at approximately half position.

    For the PSU, I have a 12V 500mA AC block...

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  • First casualties

    Yann Guidon / YGDES07/16/2017 at 21:08 0 comments

    I already damaged 2 TIL311 :-(

    I wonder what happened but I suspect my new fancy digital lab power supply. Turning it off while the circuit is still connected could send spikes that damage the pins...

    So I have to implement the power supply ASAP or I'll burn my stock of TIL311 quickly :-/

    Lesson learned : TIL311 are quite fragile...

  • References

    Yann Guidon / YGDES07/16/2017 at 10:57 0 comments

    I've been lucky to find several similar circuits on the web, as well as datasheets. Here's a list for those who are as curious as me...

    • I once found a page but it is now closed. Fortunately I saved the page "just in case" and here is the programmer's circuit:

    I'm not sure to understand most of it but it contains some interesting ideas.

    Note: this schematic applies to the 82S23 which has a particular, slower programming cycle, with a 1s pulse, limited to about 65mA (hence the series resistor and the push button), as found at :

    Yup, Vpp is also applied to the data pin, not Vcc...

    Note that current-limiting the Vpp node should be possible with a suitable base resistance...

    • Another one (source forgotten, maybe from one of the above broken links ?)

    • Another set of pictures I had saved but couldn't trace to the origin. I appreciate the (quite clumsy) translations :-)

    (ok it's obviously a translation and redrawing of the original TI datasheet but it's still nice)

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