Posted By
MMS
on 2020-06-10
17:52:16
 |  Re: Information about PCB difference, revisions of IC, historics
It is rather interesting topic.
BBC Micro used a 6502 CPU with 2MHz speed, and it was quite reliable.
The least reliable part in BBC was told to be the switch mode PSU.
It used 480mW at 2MHz. AFAIK the 7501 (based on the datasheet) requires 125 mA, at 5V it is 625mVA at 2MHz.
I do not see the benefits of the HMOS process
So the 6502 was reliable @2MHz.
But it had almost 5cm free space above CPU, which is not the case even in C16, and evidently not in +4.
So it may initiate some questions, if the main problem with the 7501/8501 CPUs are with the higher clock rate versus C64's 6510 (0.98MHz) or due to the fact that 7501/8501 has much less space and air ventillation, even compared to C64's 6510 CPU? As you can see, the C64's 6510 (@0.98MHz) is posisioned very close to the tape connector opening, so the CPU could get some fresh air via that opening.
BBC Micro's stable and reliable 6502 was also positioned to the center of motherboard in the same way as the 7501/8501 in C16.
But the 2Mhz 6502 may have a better ventillation than C16's 7501, not to mention Plus/4.
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