Motorola MVME172 - Manual (Page 337)

B
B-1
B Using Interrupts on
the MVME172
Introduction
This appendix demonstrates how to use interrupts on the MVME172. It
gives an example of how to generate and handle a VMEchip2 Tick Timer
1 interrupt on an MVME172 that has a VMEbus connection. Specific
values have been given for the register writes.
Read this entire appendix before performing any of these procedures.
VMEchip2 Tick Timer 1 Periodic Interrupt
Example
1. Set up Tick Timer:
Step Register and Address Action and Reference
1 Prescaler
Control Register
$FFF4004C If not already initialized by the
debugger, initialize as follows:
Prescaler Register = 256 - Bclock
(MHz). This gives a 1 MHz clock
to the tick timers. Bclock is the
bus clock rate, such as 25 MHz.
256 - 25 = $E7.
2 Tick Timer 1
Compare Register
$FFF40050 For periodic interrupts, set the
Compare Register value = Period
(s). For example, if you want an
interrupt every millisecond, set
the register value to 1000 ($3E8).
Refer to the
Tick Timer 1
Compare Register description in
Chapter 2.
3 Tick Timer 1
Counter Register
$FFF40054 Write a zero to clear.