USER MANUAL APS 6.0

Preface
Advanced Programming Software User Manual
4–12
Status Bit
I:0/1
Rung
B3/10 B3/12 O:0/2B3/11
1
2
3
4
]/[
B3
10
1
] [
I:0
1
( )
B3
11
( )
B3
12
2
] [
B3
11
]/[
B3
12
]/[
B3
10
( )
O:0
2
( )
B3
10
] [
I:0
1
] [
B3
11
3
4
] [
B3
11
] [
I:0
1
] [
] [
] [
( )
]/[
]/[
( )
] [
] [
] [
( )
( )
]/[
Previously, we indicated that the processor executes instructions individually , rung
by rung, from the beginning to the end of the program. This is called a program
scan and is repeated many times a second. The figure on the next page indicates in
greater detail what happens during individual scans when an external input device
(represented by I:0/1) is operated.
When the state of a bit changes during the program scan, the ef
fects this may have
in earlier rungs of the program are not accounted for until the next scan. To point
this out, we have shown successive scans (1000 and 1001, 2000 and 2001, etc.).