Another way to test for a bugged ROM apparently.

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Moggy
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Another way to test for a bugged ROM apparently.

Post by Moggy »

Found this in a copy of Sync magazine (page 9) and wondered which of the early ROMs ROM it refers to (550 or 622.) unable to test myself as all mine are fitted with Big Bang EPROMs which show 2^32 in E notation anyway.


https://archive.org/details/syncmagazin ... ew=theater
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1024MAK
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Re: Another way to test for a bugged ROM apparently.

Post by 1024MAK »

Using Kevin‘s excellent ZX81 emulator for iOS powered iPhones and iPads, I can confirm only the ‘550’ ROM (the first ‘bugged’ version) gives the screwy result.

The 622 and 649 both give the expected result.

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David G
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Re: Another way to test for a bugged ROM apparently.

Post by David G »

550 is the original ROM (the "unimproved" ROM), and it had several major bugs

622 is the "improved" ROM, which fixed those. However, 622 introduced a minor bug, which was then fixed in 649. As I understand it, 622 is the most infrequently found version as it was updated quickly on the production line

Bugs in 550
* INPUT bug
* Syntax checking bug
* The floating point bug ("maths" bug)

The method of checking the FP bug doesn't always work -- if the Sinclair assembly-line fix has been applied, even if the machine still has the 550 ROM

I'm guessing this is what the article from Sync January/February 1982 Volume 2 Number 1 is about?
Sinclair 8K ROM Problems?

In SYNC Notes {SYNC 1 :5) we gave a test to check whether you had received a defective ROM. The following letter from Nigel Searle will clarify this matter further:

Dear Customer:

The recent mention in Sync magazine of a possible bug in our 8K BASIC ROM could be misleading.

The correct value of 2^32 is 4,294,967,296. This is rounded to 8 significant digits and displayed as 4,294,967,300. 2^32-1 is 4,294,967,295 which, when rounded to 8 significant digits, is also displayed as 4,294,967,300.

This is the appropriate result for a computer of finite (8 digit) capacity.

The bug referred to in Sync will give 1,288,490,200 when 1 is subtracted from 2^32 (4,294,967,300). Only if your ROM has this problem should you return it to us for replacement.

Nigel H. Searle
Minor bug in 649
* PAUSE bug, but only in SLOW mode and only then sometimes

See ZX81 ROMs 3 types
Moggy
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Re: Another way to test for a bugged ROM apparently.

Post by Moggy »

QUOTE.

Minor bug in 649
* PAUSE bug, but only in SLOW mode and only then sometimes...

There is no PAUSE bug in 649, only the first two ROMS and then only in a certain set of circumstances in my experience.
David G
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Re: Another way to test for a bugged ROM apparently.

Post by David G »

thanks, i had a typo. i meant to write that 622 had the PAUSE bug, and 649 fixed all the bugs

to recap:
555 is the "unimproved" ROM
622 and 649 are the "improved" ROMs
Lardo Boffin
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Re: Another way to test for a bugged ROM apparently.

Post by Lardo Boffin »

See also this post:

https://sinclairzxworld.com/viewtopic.php?f=7&t=4721

where the 622 was found found in all 9 (at time of writing) of the beige / yellow / cream PCB issue one zeddies I have bought.
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Moggy
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Re: Another way to test for a bugged ROM apparently.

Post by Moggy »

I would say that the 649 was the least produced as the zeddy was more or less at end of life production by this time.
David G
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Re: Another way to test for a bugged ROM apparently.

Post by David G »

good to know. i write these out so i can remember and it's only partially working
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