Siemens SIMATIC S7 System Manual page 316

102BTechnology instructions
9.1 High-speed counter
You configure the parameters for each HSC in the device configuration for the CPU:
counting mode, I/O connections, interrupt assignment, and operation as a high-speed
counter or as a device to measure pulse frequency.
Some of the parameters for the HSC can be modified by your user program to provide
program control of the counting process:
● Set the counting direction to a NEW_DIR value
● Set the current count value to a NEW_CV value
● Set the reference value to a NEW_RV value
● Set the period value (for frequency measurement mode) to a NEW_PERIOD value
If the following Boolean flag values are set to 1 when the CTRL_HSC instruction is executed,
the corresponding NEW_xxx value is loaded to the counter. Multiple requests (more than
one flag is set at the same time) are processed in a single execution of the CTRL_HSC
instruction.
● DIR = 1 is a request to load a NEW_DIR value, 0 = no change
● CV = 1 is a request to load a NEW_CV value, 0 = no change
● RV = 1 is a request to load a NEW_RV value, 0 = no change
● PERIOD = 1 is a request to load a NEW_PERIOD value, 0 = no change
The CTRL_HSC instruction is typically placed in a hardware interrupt OB that is executed
when the counter hardware interrupt event is triggered. For example, if a CV=RV event
triggers the counter interrupt, then a hardware interrupt OB code block executes the
CTRL_HSC instruction and can change the reference value by loading a NEW_RV value.
The current count value is not available in the CTRL_HSC parameters. The process image
address that stores the current count value is assigned during the hardware configuration of
the high-speed counter. You may use program logic to directly read the count value. The
value returned to your program will be a correct count for the instant in which the counter
was read. The counter will continue to count high-speed events. Therefore, the actual count
value could change before your program completes a process using an old count value.
Condition codes: In the case of an error, ENO is set to 0, and the STATUS output contains a
condition code.
Table 9- 3
316
STATUS values (W#16#)
STATUS Description
0 No error
80A1 HSC identifier does not address a HSC
80B1 Illegal value in NEW_DIR
80B2 Illegal value in NEW_CV
80B3 Illegal value in NEW_RV
80B4 Illegal value in NEW_PERIOD
80C0 Multiple access to the high-speed counter
S7-1200 Programmable controller
System Manual, 11/2011, A5E02486680-05