Siemens SIMATIC S5 IP 281 Equipment Manual page 127

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6.5.3 Raeding the Counters
Counter 1 is read by reading counter value register 1 (CVR 1) and counter 2 by reading CVR 2
(synchronously). The basic setting is asynchronous.
Reading counters
The counters are read separately. The counter value in the respective
asynchronously
counter value register is retained during the first read access while the
read–out takes place.
The SYR synchronous bit in control register 3 must be "O" when the asyn–
Control register 3
Reading counters
Setting the SYR bit in control register 3 causes the counter values in both
and 2 synchro-
counter value registers to be retained simultaneously.
Both counter value registers can then be read.
The contents of CVR 1 and 2 are retained until the SYR bit is set to "O" again.
The following sequence must be adhered to for a synchronous read ac-
cess.
1. Set SYR bit to "1",
2. Read first counter value register.
3. Read second counter value register.
4. Reset SYR bit to "O".
Control register 3
7 6 5 4 3 2 1
the next read access.
7 6 5 4 3 2 1
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Operating Modes and Functions
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