Commodore 64 Reset Logic

Posted on Feb 4, 2014

U20 is a 556 timer configured as a one shot multivibrator. The output pulse width is determined by the size of R34 and C24. Pulse width = 1. 1 x R34 x C24 =. 5 seconds. The output on pin 9 is `high` active. The output of U8 is `low` active. Reset initializes all the processor logic and causes the processor to load the program counter register withthe address

Commodore 64 Reset Logic
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of the first instruction of the operating system program called the KERNAL. The starting address is stored in locations $FFFC and $FFFD. The first instruction is decode and executed giving KERNAL control of the computer operations. The reset pulse occurs when turning the power on to the computer.

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