The only supported writeable register type is a coil. Coils are limited to Boolean parameters. To write to a parameter in an SIS module use a non-secure parameter. The main usages for Boolean writes into the safety system from a third-party interface are for LSCEM resets and input bypasses.
For example, to reset an LSCEM block, configure a non-secure parameter reference wired to a PDET block and then to an exposed reset parameter of the LSCEM block of an SIS module as shown in the figure.
To manipulate the non-secure parameter reference from Modbus requires a control module running in the SIS Controller that contains the non-secure parameter source as shown in the figure.
The example's Modbus register mapping would be to the non-secure parameter source in the control module - DMS_NSM1/CEM_RESET.CV mapped to coil R100.
The non-secure parameter reference type is limited to Boolean, float, and integer. Normally when the reset parameter of an LSCEM block is written to the reset action is taken and then the reset parameter is cleared. To accommodate for this the Positive Directional Edge Trigger (PDET) block is required before the RESET.