Re: R: Pet problem ..
Date: 2000-09-26 20:22:08

Hallo Mario,

> And you have any idea for the garbage screen ??

The PET uses STATIC RAM for memory. Static RAM is made out of flipflops. The 
value of a flipflop can be random. In reality the chance that a bit is 0 is 
bigger then being a 1 but enough bits are set to get byte-values <> 0. 

The processor normally clears the memory, or better, fills it with spaces and 
then fills some bytes with certain values which forms a message on the sceen to 
be read by the user.

The electronics needed for translating the bytes into readable characters work 
INDEPENDENTLY from the processor. So seeing garbage simply means the processor 
never did the cleaning job and the rest. This menas that 1) or the processor is 
broken 2) or the program is wrong (read as ROM is damaged) 3) or something, 
like a faulty electronic part, caused the program to do other things then it is 
supposed to do. (to make it worse: 4) a combination of one of the above 
possebilities :( ) 

FYI, the video electronics in a C64 has to be programmed first. That's the main 
reason you see a black screen, and not garbage, on a not-working C64.

Groetjes, Ruud

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