Program Control Instructions
Chapter 10
10-5
Editing in a Completed Rung
Edit these instructions by performing the following steps:
1. Position the cursor over the MCR or ZCL instruction you want
to change.
2. Press either -(MCR)- or -(ZCL)- or any other appropriate instruction
type key.
3. Enter any parameters that may be required by a new instruction.
Immediate I/O update instructions interrupt the program scan to update I/O
data before the normal I/O update sequence. Use these instructions where
I/O modules interface with I/O devices that operate in a shorter time period
than the processor scan.
Important: You can have as many as 8 Immediate Input and 8 Immediate
Output instructions per rack.
Immediate Input/Immediate Output Update
An Immediate Input Update instruction interrupts the program scan to
update input image table with data from the corresponding module group.
The image table is updated before the normal I/O scan and executed each
program scan (Figure 10.3). This instruction is always considered logic
true and execution takes place whether or not other rung conditions allow
logic continuity.
Immediate I/O Update
Instructions
