Rockwell Automation 1785-Vx0B, D17856.5.9 PLC-5 VME VMEbus Programmable Controllers User Manual - Manual (Page 67)

Chapter 5
Commands
5-6
Word Command Description
0 Command word Has value 0003H
1 Response word As defined previously for all commands in common, see page 3-9.
2 Command interrupt level As defined previously for all commands in common, see page 3-9.
3 Command interrupt status/ID As defined previously for all commands in common, see page 3-9.
7 Enable If 0, handling of the specified interrupt (op interrupt level) is disabled.
If 1, handling of the specified interrupt is enabled.
13 Op interrupt level Specifies the VMEbus interrupt whose handling is to be enabled or disabled.
000 specifies no interrupt,
001 specifies interrupt level 1,
010 specifies level 2,
...,
111 specifies level 7.
When you enable an interrupt, the PLC-5/VME processor detects this
interrupt on the VMEbus, performs an 8-bit interrupt-acknowledge cycle,
and reads an 8-bit status/ID from the interrupter. The interrupt and
status/ID is then posted in the VME status file for accessibility to the
ladder program.
This mechanism allows VME interrupts to make a mark in the VME status
file in the processor. The ladder program can test this element in the status
file to determine whether or not the interrupt has occurred. This essentially
converts interrupts to polled events from the point of view of the ladder
program and thus introduces some small fixed overhead to the scan time;
but it gives the ladder program considerable flexibility in determining the
interrupt latency. For example, the ladder program can test for the
interrupt each scan, multiple times each scan (for smaller latency), or every
N scans.