View Single Post
Old 15th Sep 2019, 5:45 pm   #3
Join Date: Dec 2007
Location: Cambridge, Cambs. UK.
Posts: 24
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.
John Stark
detrain is offline