Programmer (HHP) User guide

Appendix B
Programming Reference
B–20
User Interrupt Latency
The user interrupt latency is the maximum time from when an interrupt
condition occurs (e.g., STI expires or HSC preset is reached) to when the
user interrupt subroutine begins executing (assumes that there are no other
interrupt conditions present). The following table lists interrupt conditions
and the corresponding time to execute the interrupt subroutine:
User Interrupt Condition Time to Execute
HSC preset is reached 183 µs
STI expires 74 µs
Comms link layer interrupt 644 µs
System overhead interrupt 20 µs
To calculate the user interupt latency when you are communicating with the
controller, add 664 µs to one or both of the following values:
• 183 µs
• 74 µs
For example, if you are communicating with the controller, the worst case
interrupt latency is 921 µs (644 µs + 257 µs).
To calculate the user interupt latency when you are not communicating with
the controller, add 20 µs to one or both of the following values:
• 183 µs
• 74 µs
For example, if you are not communicating with the controller, the worst
case interrupt latency is 277 µs (20 µs + 257 µs).