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SETTIM

     Purpose:  Set the system clock
Call address:  $FFDB (hex)  65499 (decimal)
Communication registers:  A, X, Y
Preparatory routines:  None
Error returns:  None
Stack requirements:  2
Registers affected:  None

Description:

A system clock is maintained by an interrupt routine that updates the clock every 1/60th of a second (one "jiffy"). The clock is three bytes long, which gives it the capability to count up to 5,184,000 jiffies (24 hours). At that point the clock resets to zero. Before calling this routine to set the clock, the accumulator must contain the most significant byte, the X index register the next most significant byte, and the Y index register the least significant byte of the initial time setting (in jiffies).

How to Use:

  1. Load the accumulator with the MSB of the 3-byte number to set the clock.
  2. Load the X register with the next byte.
  3. Load the Y register with the LSB.
  4. Call this routine.

EXAMPLE:

    ;SET THE CLOCK TO 10 MINUTES = 3600 JIFFIES
    LDA #0            ;MOST SIGNIFICANT
    LDX #>3600
    LDY #<3600        ;LEAST SIGNIFICANT
    JSR SETTIM
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