Replacements for Zx8301 / Zx 8302 / IPC

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Pr0f
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Replacements for Zx8301 / Zx 8302 / IPC

Postby Pr0f » Mon Dec 02, 2019 10:03 am

Given the fact that none of these chips are getting any easier to find, and have some shortcomings - certainly for Zx8301 and driving current monitor technology, I thought I would start a thread based on the possibilities for replacements for the above, not aimed at suggesting an absolute suggestion, but more by way of what can be done and even if there is a need for such a replacement or even a desire for it.

IPC

As I see it, the 8049 is available as an 8749 and can still be sourced, so in theory it is possible to still reproduce the original IPC, but that said, a Hermes or SuperHemes would be more desirable - but both these are rare to find now - is the source for these available? A total modern replacement is a possibility, but would be hamstrung by the oddball messaging between the QL and the IPC

Zx8302

These still turn up on eBay from time to time, but these are no longer being made or available once that source dries up - from what I see this is not a chip that fails that often, and it would be retained by anyone who'se switched to Aurora, so quite where the surplus are coming from - I don't know. If it was to be replaced - maybe in conjuction with the IPC - what would be the wish list for such a device?


Zx8301

This is harder of the 2 logic chips to find, and the one most likely to blow - seems the unprotected video outputs are a possible source of failures - and work to address that in the proposed issue 8, as a replacement part in the BBQL it is a timing criticial component too, so any replacement has a lot of specifications to adhere to. On top of that, the flat RGB output from the chip at a sligltly non standard timing of standard baseband video signal limits it's options on what monitors can be connected. I have had success with some CGA/Analog to VGA adaptors, and a SCART to HDMI has worked all be it with a bit of noise and shadowing, but this would be a good chip to find a replacement for. Adding extra video modes and colours not so straightforward - particularly if it will end up in the same 40 pin socket.


So various discussion topics -

    pin for pin compatibility?
    Maintain all existing functions?
    Improve if possible existing functions?
    Piggy back boards offering new functionallity and maintaining/replacing existing?


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Re: Replacements for Zx8301 / Zx 8302 / IPC

Postby RWAP » Tue Dec 03, 2019 5:30 am

Just to confirm - I have literally 100s of 8302 chips..... hence why I list them at a low price

I have maybe 20 8301s left in stock (after Tony Firshman hunted high and low around his house)


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Re: Replacements for Zx8301 / Zx 8302 / IPC

Postby Pr0f » Tue Dec 03, 2019 7:43 am

That's good to know Rich - so the ZX8301 is the more ciritically endangered species then! ;-)

Are SuperHermes still available? I see the odd Hermes coming up on retro...


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Re: Replacements for Zx8301 / Zx 8302 / IPC

Postby RWAP » Wed Dec 04, 2019 11:08 am

Pr0f wrote:That's good to know Rich - so the ZX8301 is the more ciritically endangered species then! ;-)

Are SuperHermes still available? I see the odd Hermes coming up on retro...


Yes 8301s are a big problem.

No superHERMES unfortunately - Tony Firshman keeps trying to make a new batch for me, but he has not been able to get them working properly - one of the main problems is that he didn't document anything!

Rich


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Peter
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Re: Replacements for Zx8301 / Zx 8302 / IPC

Postby Peter » Wed Dec 04, 2019 12:13 pm

Pr0f wrote:That's good to know Rich - so the ZX8301 is the more ciritically endangered species then! ;-)

Maybe an additional reason for a SGC successor with onboard video. Like the (S)GC freeing 68008, also freeing the ZX8301 and making it available for more "needy" BBQLs.

My memory is just to rusted to tell without look at the QL schematics, whether removing the ZX8301 would require extra tricks. Probably not.


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Re: Replacements for Zx8301 / Zx 8302 / IPC

Postby Dave » Sat Dec 07, 2019 6:46 pm

When we talk 8301 we're really talking video.

When we talk 8302/8049 we're really talking a register block used for assorted IO, that are quite easy to replicate from the register side, but harder from the IO side unless we let some things go like microdrives.

There's a lot of room for improvement in both of these, but they're also very different problems.

For the 8301, I have used a Seiko Epson video IC and dual port RAM to recreate QL modes (excluding flash). This is fussy, but it mostly works and does nicely solve the modern output problem. That said, it is not a perfect solution - it's just a bodge.

For the 8302/8049, a larger ATMega controller can duplicate most of the functionality, but it's just a bit too slow. Our thinking was to put whatever replaced the 8302/8049 behind 1K or 2K of dual port SRAM so they could operate asynchronously, but I never got to make progress with that work. I do have all the ICs and some designs though.

I did sign up for a VHDL course at the local university, as an FPGA would provide the "ideal" solution, but unfortunately I did not thrive in that class and decided to drop out because the lecturer's teaching style was by wrote, and I am a visual learner.


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Re: Replacements for Zx8301 / Zx 8302 / IPC

Postby Peter » Sat Dec 07, 2019 11:12 pm

Dave wrote:I did sign up for a VHDL course at the local university, as an FPGA would provide the "ideal" solution, [...]

Wondering why VHDL was offered in the U.S., I thought VHDL was more or less a European specialty.
Verilog is better if you like the hardware descriptions short and legible, like me.

The non-ideal thing with FPGAs are the various supply voltages and lack of 5V tolerance.


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Re: Replacements for Zx8301 / Zx 8302 / IPC

Postby Dave » Tue Dec 10, 2019 1:20 am

I have a bunch of 68SEC000 that can run at 40MHz or more, and that are 3.3V capable. So it's a small step to do a fully 3.3V QL - though I have no personal plans to do that.



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