1) UDC 3300 has Modbus RTU (RS-485) only, no ethernet option.
The UDC 2500 or UDC 3200 can have the Ethernet card that does Modbus-over-Ethernet.
The HC-900 has two RS-485 serial ports, either of which can be configured as a Modbus master to send SP's to a UDC.
2) A UDC can only handle a single (one) variable written to it in a single transaction. So writing a setpoint is the simple and easy way to accomplish what you want to do.
Attempting to write an entire setpoint profile to a UDC is very complicated, because only one setpoint programmer/profile datum can be written per transaction, requiring multiple transactions to populate a UDC SP profile.
3) Pay NO attention to any of the information (registers, addresses, function codes) given in the UDC Product Manuals, section 9, Modbus RTU function codes. Those function codes are for undocumented functions 20 and 21 (decimal). This information is totally useless, disorienting and confusing.
Honeywell publishes a manual, document # 51-52-25-66, called the Modbus® RTU Serial Communications User Manual, which has correct information.
4) Limit the number write functions of repeated data, because the internal memory gets overwritten every time a write value is received, so that in power up after power down situation, the last known working variables are available. The internal memory has a limitation as to the number of writes it can handle.
So only write the setpoint at the beginning of a soak, do not write the soak value every couple seconds on a continuous basis or the memory will fail from fatigue.
5) There are separate integer registers and separate floating point registers in the UDCs, so pick the correct register for the word format that you select.
6) If it were me, I'd just use the HC-900.
