Purpose: Increment internal clock
Call address: Call address: $FFEA (hex) 65514 (decimal)
Registers: none Memory: system map Flags: none Calls: noneResults:
Registers: .A used .X used Memory: TIME, TIMER, STKEY updated Flags: none
Description: UDTIM increments the system software (jiffie) clock, which counts sixtieths (1/60) of a second when called by the system 60Hz IRQ. TIME, a 3-byte counter located at $A0, is reset at the 24-hour point. UDTIM also decrements TIMER, also a 3-byte counter, located at $AlD (BASIC uses this for the SLEEP command, for example). You should be sure IRQ's are disabled before calling UDTIM to prevent system calls to UDTIM while you are modifying TIME and TIMER. UDTIM also scans key line C7, on which the STOP key lies, and stores the result in STKEY ($91). The Kernal routine STOP utilizes this variable.
SEI JSR $FFEA ;UDTIM CLI