what ROM do I have?

Discussions about Sinclair ZX80 and ZX81 Hardware
sl07h1
Posts: 34
Joined: Mon Feb 22, 2021 7:16 pm

what ROM do I have?

Post by sl07h1 »

I learned that there are two ROMs, a first, buggy one and a newer (less older, :D ) debugged one. There's an easy way to know what ROM I have, a PEEK on an address or something?

If I have the buggy ROM, should I worry?

Thanks in advice!
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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: what ROM do I have?

Post by 1024MAK »

Err, we now know that there are THREE different ZX81 ROMs that were used in production ZX81s. See this topic. There is also a test program later on in that topic.

In addition, the first ROM, the one with the maths bug, ZX81s can have an extra circuit fitted that “intercepts” the data when the Z80 reads the dodgy part of the bugged ROM, this kinda corrects the maths bug. There is a bit of information about this here (but I have not yet updated this with the recent discovery of the third ROM).

So in total, that’s FOUR variations.

Here is a BASIC test program (courtesy of Moggy):

10 FAST
20 LET A = 0
30 FOR B = 0 TO 8191
40 LET A = A + PEEK B
50 NEXT B
55 PRINT “ROM TEST”
60 PRINT A
70 PRINT SQR 0.25

Note that it takes a while and while running, you will get a black screen.

Note the numbers it reports and report what it says.

Mark

Ref: ROMchip version test
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
Moggy
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Re: what ROM do I have?

Post by Moggy »

I know I'm old fat and silly but I honestly cannot remember supplying that ROM checker. :oops:


If it is an NEC ROM then the it should be numbered either 550-(early bugged ROM) 622-(cured maths bug but supposedly faulty pause routine) 649-(last of the line bugs ironed out albeit not quite accurate with how numbers are held but can be worked around from BASIC)
Last edited by Moggy on Wed Mar 17, 2021 2:18 pm, edited 1 time in total.
sl07h1
Posts: 34
Joined: Mon Feb 22, 2021 7:16 pm

Re: what ROM do I have?

Post by sl07h1 »

1024MAK wrote: Wed Mar 17, 2021 10:35 am
10 FAST
20 LET A = 0
30 FOR B = 0 TO 8191
40 LET A = A + PEEK B
50 NEXT B
55 PRINT “ROM TEST”
60 PRINT A
70 PRINT SQR 0.25

Note that it takes a while and while running, you will get a black screen.

Note the numbers it reports and report what it says.

Mark
ROM TEST
855106
0.5
Moggy
Posts: 3231
Joined: Wed Jun 18, 2008 2:00 pm

Re: what ROM do I have?

Post by Moggy »

That checksum is for the 2nd ROM issue 622. Division bug cured but supposedly having a fault which causes the listing to program vanish when PAUSE used without a suitable following POKE.

I only observed this once and try as I might cannot get it to manifest itself again.
sl07h1
Posts: 34
Joined: Mon Feb 22, 2021 7:16 pm

Re: what ROM do I have?

Post by sl07h1 »

I read the other post, it seems that I have the NEC ROM 622 (checksum 855106)

Thanks a lot!
Moggy
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Joined: Wed Jun 18, 2008 2:00 pm

Re: what ROM do I have?

Post by Moggy »

For reference the three ROM types checksums.

550-854885

622-855106

649-878117
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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: what ROM do I have?

Post by 1024MAK »

ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
Moggy
Posts: 3231
Joined: Wed Jun 18, 2008 2:00 pm

Re: what ROM do I have?

Post by Moggy »

I am seriously doubting my sanity as I have no remembrance of this at all. :( :oops:
bola_dor
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Joined: Wed Oct 02, 2019 5:32 am

Re: what ROM do I have?

Post by bola_dor »

Moggy wrote: Wed Mar 17, 2021 2:29 pm For reference the three ROM types checksums.

550-854885

622-855106

649-878117
Well I have this ROM
20210402_194409.jpg
Placed on a CZ1500 (Argentinian Timex Portugal rebranded TS1500) .
16174036062198651357705092683647.jpg
With this result:
20210402_194357.jpg
Then I thought it would be a 649 but I have a 622 checksum result.. :? :?:
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
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