Anchal mentioned it would be good to put more details about how I arrived at the values needed to configure the modbus drive for the temperature sensor, since this information is not in the manual and is hard to find on the internet, so here is a breakdown.
So the generic format is:
which in our case become:
As can be seen, the parameters of the first two functions "drvAsynIPPortConfigure" and "modbusInterposeConfig" are straight forward, so we restrict our discussion to the case of third function "drvModbusAsynConfigure". Well, after hours of trolling the internet, I was able to piece together a coherent picture of what needs doing and I have summarised them in the table below.
Once the asyn IP or serial port driver has been created, and the modbusInterpose driver has been configured, a modbus port driver is created with the following command:
drvModbusAsynConfigure(portName, # used by channel definitions in .db file to reference this unit)
tcpPortName, # reference to portName created with drvAsynIPPortConfigure command
modbusLength, # length in dataType units
pollMsec, # how frequently to request a value in [ms]
Modbus addresses are specified by a 16-bit integer address. The location of inputs and outputs within the 16-bit address space is not defined by the Modbus protocol, it is vendor-specific. Note that 16-bit Modbus addresses are commonly specified with an offset of 400001 (or 300001). This offset is not used by the modbus driver, it uses only the 16-bit address, not the offset.
For ServersCheck, the offset is "30001", so that
modbusStartAddress = 30200 - 30001 = 199