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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 14th Sep 2019, 1:01 pm   #1
McMurdo
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Default Commodore 64 tape motor control

Something I've always wondered, why do some cassette programs leave the tape motor on even though the program has loaded? It just happens with certain commercial games I have. It's always done it and always specific games. Even when the end of the tape is reached and the play key flicks up, the motor still runs.
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Old 14th Sep 2019, 2:26 pm   #2
Richard_FM
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Default Re: Commodore 64 tape motor control

Quote:
Originally Posted by McMurdo View Post
Something I've always wondered, why do some cassette programs leave the tape motor on even though the program has loaded? It just happens with certain commercial games I have. It's always done it and always specific games. Even when the end of the tape is reached and the play key flicks up, the motor still runs.
I remember my 128 used to do that when a games cartridge was plugged in.

I'm guessing some programs would trigger the tape run flag & not turn it off for some reason.
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Old 15th Sep 2019, 6:45 pm   #3
detrain
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Default Re: Commodore 64 tape motor control

It happened because of misprogramming of the I/O port at address $0001. Bits 0-2 controlled the memory map and bits 3-5 the cassette - bit 5 turned the motor on.

Most games used this I/O port to switch out the BASIC or KERNAL ROMs to use the RAM at their addresses, or to map the character font ROM into the CPU address space to copy the built-in font and redefine some of the characters. If they didn't mask the bits correctly they could mistakenly turn the cassette motor on.
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