ZX Spectrum 48K ULA differences

Updated: 5 August 2021

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I’ve often wondered what the differences between the ULA models for the ZX Spectrum are.
Fortunately Chris Smith did a brilliant job of writing a comprehensive technical masterpiece about the ZX Spectrum’s ULA and its history.

Underneath a short summery of the different ULA models and in which ZX Spectrum issues they were used:

  • 5C102E: ZX Spectrum Issue 1 boards
  • 5C112E: ZX Spectrum Issue 2 boards
  • 6C001E-5: the first 6000 series ULA, probably for ZX Spectrum Issue 3 boards (not documented in Chris Smith’s book)
  • 6C001E-6: ZX Spectrum Issue 3 boards
  • 6C001E-7: ZX Spectrum Issue 4A boards (and higher board issues)

For the exact differences I recommend to buy “The ZX Spectrum ULA – How To Design A Microcomputer” (ISBN 978-0-9565071-0-5) by Chris Smith yourself.
But for ZX Spectrum enthousiast like myself who need to know about compatibility:

  • The 6C001E-7 ULA version can be used on all ZX Spectrum 48K board issues.
  • The ZX Spectrum Issue 4A and above will ONLY work reliable with the 6C001E-7 ULA version; don’t use another ULA in an Issue 4A board or later Issue.

Of course it’s best to use the exact ULA model that corresponds to the ZX Spectrum Issue as listed above; ULA’s are getting more rare each day.


Update 5 August
Mark K sent me this info, about the ‘dead cockroach’ mod for 5C102E ULAs, and ‘spider’ mod on issue 2 boards:

Basically, whatever board (issue one or issue two) the 5C102E ULAs are used in, the ‘dead cockroach’ daughter board is required.
All ULA versions from the 5C112E onwards incorporated the correction for the ‘dead cockroach’ internally in the ULA, hence the ‘dead cockroach’ daughter board is no longer required.

The transistor ‘spider’ should also have been fitted, but at the time these ULAs were being used, the problem that this fixes had not been discovered.
All issue two boards regardless of which ULA is used, should have the transistor ‘spider’ fitted.
All boards from the issue three onwards have the ‘spider’ transistor included on the PCB (TR6) so no separate ‘spider’ transistor is needed.

More info can be found in this topic: https://spectrumcomputing.co.uk/forums/viewtopic.php?p=71331#p71331


2 thoughts on “ZX Spectrum 48K ULA differences

  1. And,would it be worth mentioning on this page which of these ULA’s use which work-arounds (dead spider, cockroach, maybe others)? Then we have it all complete on one location 😉

    • Hmm, good one, but do you know if that information is gathered somewhere already? Otherwise I’ll have to ask others for it as I’ve not worked on that many boards with e.g. the cockroach.

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