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| | Previous Messages | Posted By
Paulk
on 2021-07-13
03:53:41
|  Re: 7501 & 8501 Again
Yes I took the chips out that I could and re-seated them and now it is displaying the correct amount of memory and working perfectly. I have not been able to replicate the same fault with the 7501 but it's all working so I am happy 
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Posted By
TLC
on 2021-07-12
14:34:05
| Re: 7501 & 8501 Again
@PaulK : possibly you have a pair of "partially working" (or, partially bad, whichever you'd prefer) chips. Sometimes an internal defect only manifests in just breaking some parts of the chip, rather than rendering the whole part defective. I also have, for example, one 8501 chip, which irregularly fails to drive one of the outputs of the onboard port. I've also had a dozen of TEDs with various nuisances; one that had an attribute bit stuck so everything was just always shown in colours; another one that failed to blank the upper and bottom 4 scanlines of the screen area on clearing bit 3 of $ff06 ( ---> vertical smooth scroll always showed garbage in the upper and bottom part of the screen), and so on. Sometimes this happens. Symptoms can be completely random , according to how the partial defect has manifested. It may sometimes only affect some analog property, who knows. This is not a general difference of "the" 7501 and 8501 chips. To know more, you'd have to test the chips in some known-to-be-perfectly-working machine.
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Posted By
Hifi
on 2021-07-10
15:10:56
| Re: 7501 & 8501 Again
Helló,helló ÚJRA Itt vagyok...... Már többször volt erről szó....... A MOS7501/MOS8501 CPU TELJESEN azonos!!! Programozás, opkódok ill. illegális opkódokban is teljesen AZONOSAK! CSAK technológia gyártásban különböznek, a 7501-HMOS-1, a 8501-HMOS-2 félvezető technológiával lett gyártva! A C64-ben lévő MOS6510 (MOS6502 egyik változata...) még NMOS technológiával volt gyártva. Az "aljas kapitalista" gyártók ezzel az ÚJABB technológiával tették ÓLCSÓBBÁ a CPU gyártását!!! NEM akarok senkit megsérteni, DE aki elektronikához ,pláne számítástechnikához nyúl, vagy tudja, hogy mit csinál, vagy bízza SZAKEMBERRE!!! ENNYI! Üdv.: HiFiofTLT
| Re: 7501 & 8501 Again
Hello, hello, here I am again... I've talked about this before several times... The MOS7501 / MOS8501 CPUs are COMPLETELY IDENTICAL !!! Programming, opcodes including illegal opcodes, they are exactly THE SAME! They differ only in technology production, the 7501-HMOS-1, 8501-HMOS-2 were manufactured with semiconductor technology! The MOS6510 which is in the C64 (a version of MOS6502...) was still manufactured with NMOS technology. The "vile capitalist" manufacturers have made the production of the CPU CHEAPER with this NEWER technology !!! I DON'T want to offend anyone, BUT if touch any electronics, especially computers, either they should know what they are doing, or entrusts it to a PROFESSIONAL !!! THAT'S ALL! Bye: HiFiofTLT
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Posted By
PaulK
on 2021-07-09
12:38:53
| 7501 & 8501 Again
I have read through quite a few threads and it is stated that there is no real difference between the 7501 and 8501 cpu's. My cassette recorder would not work with my Plus 4 even though fuse etc all ok so I took a 7501 from a c16 and now it works fine on my plus 4 but now the memory is not displayed correctly on start up. It only shows 12277 but with the 8501 it displays the correct amount. Typing print fre(0) also displays the wrong memory amount with the 7501 fitted.
So is there something else wrong with the plus 4 if these cpu's work the same?
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