User Manual

Programming made easy
6.6 High-speed counter (HSC)
Easy Book
Manual, 03/2014, A5E02486774-AF
119
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. Setting the following Boolean flag values to 0 results in no change.
● Setting DIR = 1 loads a NEW_DIR value.
● Setting CV = 1 loads a NEW_CV value.
● Setting RV = 1 loads a NEW_RV value
● Setting PERIOD = 1 loads a NEW_PERIOD value.
6.6.1
Operation of the high-speed counter
High-speed counters (HSC) can count events that occur faster than the cyclic OB execution
rate. If the events to be counted occur slower than the execution rate of the OB, you can use
CTU, CTD, or CTUD standard counter instructions. If the events occur faster than the OB
execution rate, then use the faster HSC device. The CTRL_HSC instruction allows your
program to programmatically change some of the HSC parameters.
For example: You can use the HSC as an input for an incremental shaft encoder. The shaft
encoder provides a specified number of counts per revolution and a reset pulse that occurs
once per revolution. The clock(s) and the reset pulse from the shaft encoder provide the
inputs to the HSC.
The HSC is loaded with the first of several presets, and the outputs are activated for the time
period where the current count is less than the current preset. The HSC provides an interrupt
when the current count is equal to preset, when reset occurs, and also when there is a
direction change.
As each current-count-value-equals-preset-value interrupt event occurs, a new preset is
loaded and the next state for the outputs is set. When the reset interrupt event occurs, the
first preset and the first output states are set, and the cycle is repeated.
Since the interrupts occur at a much lower rate than the counting rate of the HSC, precise
control of high-speed operations can be implemented with relatively minor impact to the scan
cycle of the CPU. The method of interrupt attachment allows each load of a new preset to be
performed in a separate interrupt routine for easy state control. Alternatively, all interrupt
events can be processed in a single interrupt routine.