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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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14th Sep 2019, 1:01 pm | #1 |
Dekatron
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,273
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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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Kevin |
14th Sep 2019, 2:26 pm | #2 | |
Nonode
Join Date: Sep 2017
Location: Stockport, Cheshire, UK.
Posts: 2,004
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Re: Commodore 64 tape motor control
Quote:
I'm guessing some programs would trigger the tape run flag & not turn it off for some reason.
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Hello IT: Have you Tried Turning It Off & On Again? |
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15th Sep 2019, 6:45 pm | #3 |
Triode
Join Date: Dec 2007
Location: Cambridge, Cambs. UK.
Posts: 37
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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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John Stark |