Motorola MVME1X7P User Manual

Programming Model

http://www.motorola.com/computer/literature

3-19

The Tick Timer 1 Counter is a 32-bit read/write register located at address 
$FFF42008. When enabled, it increments every microsecond. Software 
may read or write the counter at any time.

The Tick Timer 2 Compare Register is a 32-bit register located at 
$FFF4200C. The count value of Tick Timer 2 is compared to this register. 
When they are equal, an interrupt is sent to the Local Bus interrupter and 
the overflow counter is incremented. If the clear-on-compare mode is 
enabled, the counter is also cleared. For periodic interrupts, the following 
equation should be used to determine the compare register value for a 
specific period.

compare register value = T (

µ

s) 

When programming the tick timer for periodic interrupts, the counter 
should be cleared to zero by software and then enabled. If the counter does 
not initially start at zero, the time to the first interrupt may be longer or 
shorter than expected. The rollover time for the counter is 71.6 minutes.

31

. . .

0

Tick Timer 1 Counter

R/W

X

31

. . .

0

Tick Timer 2 Compare Register

R/W

0 P