what ROM do I have?
what ROM do I have?
I learned that there are two ROMs, a first, buggy one and a newer (less older, ) 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!
If I have the buggy ROM, should I worry?
Thanks in advice!
- 1024MAK
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Re: what ROM do I have?
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
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.
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.
Re: what ROM do I have?
I know I'm old fat and silly but I honestly cannot remember supplying that ROM checker.
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)
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.
Re: what ROM do I have?
ROM TEST
855106
0.5
Re: what ROM do I have?
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.
I only observed this once and try as I might cannot get it to manifest itself again.
Re: what ROM do I have?
I read the other post, it seems that I have the NEC ROM 622 (checksum 855106)
Thanks a lot!
Thanks a lot!
Re: what ROM do I have?
For reference the three ROM types checksums.
550-854885
622-855106
649-878117
550-854885
622-855106
649-878117
- 1024MAK
- Posts: 5153
- Joined: Mon Sep 26, 2011 10:56 am
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Re: what ROM do I have?
Other relevant links:
Test ROM program
And presumably where this program originated
ZX81 Versions/Issues
Topic with photos of the extra board to correct the ROM bug
Mark
Test ROM program
And presumably where this program originated
ZX81 Versions/Issues
Topic with photos of the extra board to correct the ROM bug
Mark
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.
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.
Re: what ROM do I have?
I am seriously doubting my sanity as I have no remembrance of this at all.
Re: what ROM do I have?
Well I have this ROM Placed on a CZ1500 (Argentinian Timex Portugal rebranded TS1500) . With this result:
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
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