It is recommended that you limit the number of periodic writes to all static or non-volatile parameters such as HI_HI_LIM, LOW_CUT, SP, TRACK_IN_D, OUT, IO_OPTS, BIAS, STATUS_OPTS, SP_HI_LIM, and so on. Static parameter writes increment the static revision counter, ST_REV, and are written to the device's non-volatile memory. Fieldbus devices have a non-volatile memory write limit. If a static or non-volatile parameter is configured to be written periodically, the device can stop its normal operation after it reaches its limit or fail to accept new values. Consult the device documentation to determine if a parameter is static or non-volatile.
Another way to configure your system to avoid burning out non-volatile memory is to link a CALC block or PID block running in the controller to the AO block running in the device. This method avoids the use of asynchronous writes by writing to the AO block through a publisher/subscriber mechanism.
To link a CALC block to the AO block
Set the AO block mode to CAS, AUTO, or MAN.
Link the CALC block's OUT parameter to the AO block's CAS_IN parameter.
To link a PID block to the AO block
Set the AO block mode to CAS, AUTO, or MAN.
Link the PID block's OUT parameter to the AO block's CAS_IN parameter.
Link the AO block's BKCAL_OUT parameter to the PID block's BKCAL_IN parameter.
Set the PID parameter CONTROL_OPTS to Track Enable.
Write a value to the AO block using the TRK_IN_D and TRK_VAL parameters.