GE 90-30/20/Micro manual PLC Sweep

2

All of these steps execute every sweep. Although the Programmer Communications Window opens each sweep, programmer services only occur if a board fault has been detected or if the programming device issues a service request; that is, the Programmer Communications Window first checks for work to do and exits if there is none. The sequence of the standard program sweep is shown in the following figure.

START-OF-SWEEP HOUSEKEEPING

I/ONO ENABLED

?

YES

INPUT SCAN

RUN NO MODE

?

YES

LOGIC SOLUTION

I/ONO ENABLED

?

YES

OUTPUT SCAN

PROGRAMMER COMMUNICATIONS

SYSTEM

COMMUNICATIONS

USER PROGRAM

CHECKSUM

CALCULATION

HOUSEKEEPING

DATA

INPUT

PROGRAM

EXECUTION

DATA

OUTPUT

PROGRAMMER

SERVICE

SYSTEM

COMMUNICATIONS

DIAGNOSTICS

a43064

SCAN

TIME

OF

PLC

START NEXT SWEEP

Figure 2-1. PLC Sweep

GFK-0467K Chapter 2 System Operation 2-3