ICL OPD

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Pr0f
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Re: ICL OPD

Postby Pr0f » Sat Jun 15, 2019 10:53 am

keyboard is very weird - I actually have an ICL OPD keyboard from long ago, which I picked up from a surplus place in Bedford when I lived there.

So I can spend some time bussing out the matrix - the actual keyboard matrix driver is using one out and one in 8 bit shift registers - although I think there may also be some 'extra' keys based on the keyboard tail and socket. I am going to find out which chip on the board provided the serial data streams in and out - I suspect it will be the custom ULA3 which ICL provided, as that handles some I/O decode and provide the main serial port for the inbuilt modem / telephone unit. At the very least, removing the shift registers would give access to the full matrix, so making it possible to use a parallel accessed keyboard.

As far as I can tell from some quick look and see, the ZX8302 is used to drive the Microdrives, provide the RTC (although they reference the 1st of Jan 1970 as second 0), and provide an out only serial port for the printer. I have yet to determine if the IPC connections are used for it. The ZX8302 gets a full 64K of address space to live in - so no additional decoding is done in that space to restrict port usage - they are just using the decode logic in the Zx8301.

Apart from the circuit diagram, the only thing I can't find much info on is the speech chip, which uses a ROM with set phrases on - that ROM is on the main board, but the speech processor is on the processor mezzanine board.

The processor board also holds 4 x 32K ROM's for the OS and other utilities, decoded in a rather odd way (an LS138 with A15, A17 and A19 going to the address inputs, and A16 and A18 fed to the active low enables) I have figured out that by swapping to address lines A19 and A16, I can have the ROM's all starting from 0-1EFFF, and will have to provide some kind of decoded signal to prevent ROM access when the ZX8302 is addressed. A job for a GAL I think, that can decode out the Zx8302, a serial chip, and an IDE and or floppy interface. I plan on adding in a 512K CMOS RAM somewhere in the mix too - and then leaving the top 256K for the application ROMs and other bits. It's a weird way to get a QL, but it has half the work of customising already done, and the chaps from ICL left lot's of spare space around the board to put additional ROM or other goodies into.


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Pr0f
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Re: ICL OPD

Postby Pr0f » Mon Jun 24, 2019 3:56 pm

Attached is a PDF with some further info gained by some reverse engineering on the boards I have.
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opd decoding.pdf
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Ralf R.
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Re: ICL OPD

Postby Ralf R. » Mon Jun 24, 2019 4:08 pm

Very interesting to read. As far as I remember, I have read elsewhere, that there was indeed a floppy I/F for the OPD. Would be interesting to see, how it works at software side.


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Pr0f
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Re: ICL OPD

Postby Pr0f » Wed Jun 26, 2019 9:09 am

I forgot to add in my diagnosing that the keyboard for the OPD is handled by 2 shit registers, and the clock, clear, shift data in and out and the parallel load are all signals routed to the off board modem / telco unit. This has an on board 8051 chip which appears to be handling the reading of the keyboard, and it communicates back to the main board via the 4 lines coming from ULA3 chip.

Given that this chip has only the lowest 4 data lines fed to it, the protocol is probably no better than the ZX8302 mechanism. I am sorely tempted to feed the ZX8302 IPC lines out to the 32 pin connector, and then place a propeller or a PIC there to handle reading of the keyboard and provide serial ports / sound.


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vanpeebles
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Re: ICL OPD

Postby vanpeebles » Thu Jun 27, 2019 8:12 am

I take it those two registers are not very good? :lol: :lol:


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Pr0f
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Re: ICL OPD

Postby Pr0f » Thu Jun 27, 2019 8:54 am

vanpeebles wrote:I take it those two registers are not very good? :lol: :lol:


oops - I love a good typo in the morning....


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Pr0f
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Re: ICL OPD

Postby Pr0f » Thu Jun 27, 2019 9:06 am

This is pretty much the circuit used in the OPD:

http://www.openmusiclabs.com/learning/d ... index.html

There are 2 extra lines on the 20 pin ribbon from the keyboard, that I think carry keypress details for specific functions keys on the keyboard (resume, etc) and are not part of the 8x8 matrix.

I will spend some time diagnosing the keyboard map - but will be after the weekend, as I've got a busy one coming up...



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