Rockwell Automation 1772-AF1,D17726.5.1 User Manual MINI-PLC-2/15 - Manual (Page 11)

Programming
Chapter 3
3Ć3
To guard against improper program execution, automatic check routines are
incorporated in the AF1. The processor uses these routines to prevent the
following:
Executing AF1 functions having invalid function addresses
Spending so much time executing AF1 functions that the controller neglects
its main program and I/O scans
Invalid Function Addresses
Valid AF1 function addresses include the I/O image table and the data table
(except word 027). Specifically, valid addresses are from 010 to 026, from 030
to 077, and from 110 to the end of the data table. Result addresses must not
reside in the input image table.
When a user programmed function has an invalid address, the response of the
processor depends upon whether the keyswitch is in the RUN or
RUN/PROGRAM position.
The responses are:
In the RUN position, the processor stops running and the CRT displays
PROCESSOR FAULT and CHANGE PROCESSOR TO PROGRAM MODE.
The processor and memory LEDs illuminate. After you change processor
operation to program mode the LEDs turn off and the CRT displays MODE
SELECTION menu and PLC-2 RUN TIME ERROR, PRESS 11 TO
CONTINUE. When you press 11 the CRT displays and intensifies the rung
containing the illegal address and states ILLEGAL ADDRESS INTENSIFIED
INSTRUCTION LINKED WITH CAUSE OF ERROR.
In the RUN/PROGRAM position, the processor stops running and the CRT
displays MODE SELECTION menu and PLC-2 RUN TIME ERROR, PRESS
11 TO CONTINUE. When you press 11 the CRT displays and intensifies the
rung containing the illegal address and states ILLEGAL ADDRESS
INTENSIFIED INSTRUCTION LINKED WITH CAUSE OF ERROR.
Avoiding Excessive AF1 Execution Times
Table 3.B lists execution times for AF1 functions. To avoid excessive AF1
function execution times, an interlock system is designed into the AF1. This
system automatically checks and does the following:
Permits no AF1 function to run longer than 6ms without returning processor
scan to the processor.
During a program scan each true AF1 function rung which can be completed
in a single scan will be completed as it is encountered. However, upon
encountering a true AF1 function rung which requires multiple program scan
AF1 Automatic Checks