Siemens CPU 948 - Page 118

Counter operations
(continued)
I 4.0
RSCI
-
binary
16 bits
CU
BI
DE
RQ
C1
CD
S
CV
Owing to the two separate edge flags for CU and CD,
a counter with two different inputs can be used as an
up/down counter.
The value of the addressed counter is decremented
by 1 to a maximum counter value of 0. The function
is only executed on a positive edge (from "0" to "1")
of the logic operation programmed before the CD.
The flags necessary for edge evaluation of the
counter inputs are incorporated in the counter word.
I 4.0
A
I
4.0
CD C 1
CU
BI
DE
RQ
C1
CD
S
CV
I 4.0
CQ
Logical/circuit diagram
STEP 5 representation
Ladder Control system
Statement
list
Count down
diagram flowchart
Programming Examples in the STL, LAD and CSF Methods of Representation
CPU 948 Programming Guide
3 - 46 C79000-G8576-C848-04