I have several Honeywell UDC5300 Controllers (circa 1998) with the Serial Communication option (verified installed). None of the controllers are responding to serial communications. Three controllers have been tested and all fail to communicate with the Master.

Efforts to date to establish serial communication:

Controller: Each controller has had the Configuration Reset (CLR CFG), "SER COMM" parameters programmed, Serial termination set (testing one controller at a time) and wired full duplex (2 twisted shielded pairs) to the Master as shown in the Honeywell User Manual. The chassis is connected to the power ground, the Controller and PC chassis are connected through the shields and TB 1 - terminal 8 is connected to the controller chassis as shown in the Honeywell User Manual.

Client (Master): Using Modbus Poll as the Master for these tests. The Master communicates properly with Modbus Slave (Server) over both an internal PC virtual serial connection and external PC hardware serial connections. All the serial parameters match the Controller settings. When a request for Coil Data (or any other Function) is sent by the Master, there is no response transmitted from the Controller. The Master Messages match the format, data and calculated checksum as defined the Honeywell's "Modbus® RTU Serial Communications User Manual"

The hardware serial interface is comprised of a Windows PC, an FDTI USB to TTL cable and a TTL to RS-422 interface board. Using a terminal program, the hardware channel echoed back the sent data with the RS-422 looped back on itself. The receive side of the RS-422 interface board is terminated with a 120 ohm resistor. No flow control is selected as only the TxD and RxD lines go to the RS-422 interface board.

Honeywell's "Modbus® RTU Serial Communications User Manual" (51-52-25-66) identifies an UDC5300 specific "Communication and Configuration User Manual" (51-52-25-68), but I have not located a copy.

Does anyone recall a Master/Slave handshake (or other tricks) to initiate serial communications with the UDC5300?

Thanks in advance for your help.

John

 

see attached

 

UDC5300 was a Leeds & Northrup product, inherited when Honeywell bought L&N. Make sure the controller is configured for Modbus, not Binary (a proprietary L&N Protocol), page 356, user manual

UDC5300 has internal jumpers to enable RS-485 terminating resistors. See pages 358, 359 in the user manual (attached)

I'd tend to jumper Rx- to Tx-, Rx+ to Tx+ and run it 2 wire 485 instead of 4 wire because Modbus is inherently half duplex. USB/485 FTDI converters are only about $30.

Remember that (+) and (-) driver lines are defined differently by different vendors. Try swapping the driver leads at one end in case such is the case.

 

see attached

Thanks, will dive in.

 

UDC5300 was a Leeds & Northrup product, inherited when Honeywell bought L&N. Make sure the controller is configured for Modbus, not Binary (a proprietary L&N Protocol), page 356, user manual

UDC5300 has internal jumpers to enable RS-485 terminating resistors. See pages 358, 359 in the user manual (attached)

I'd tend to jumper Rx- to Tx-, Rx+ to Tx+ and run it 2 wire 485 instead of 4 wire because Modbus is inherently half duplex. USB/485 FTDI converters are only about $30.

Remember that (+) and (-) driver lines are defined differently by different vendors. Try swapping the driver leads at one end in case such is the case.

Thanks, the controllers came with a hardcopy manual (an unusual luxury these days) and I have set the Protocol to Modbus.

I have a converter as you describe above and I am following your suggestion above on wiring and checkout.

Will post again after the test.

 

Thanks, the controllers came with a hardcopy manual (an unusual luxury these days) and I have set the Protocol to Modbus.

I have a converter as you describe above and I am following your suggestion above on wiring and checkout.

Will post again after the test.

UDC5300 was a Leeds & Northrup product, inherited when Honeywell bought L&N. Make sure the controller is configured for Modbus, not Binary (a proprietary L&N Protocol), page 356, user manual

UDC5300 has internal jumpers to enable RS-485 terminating resistors. See pages 358, 359 in the user manual (attached)

I'd tend to jumper Rx- to Tx-, Rx+ to Tx+ and run it 2 wire 485 instead of 4 wire because Modbus is inherently half duplex. USB/485 FTDI converters are only about $30.

Remember that (+) and (-) driver lines are defined differently by different vendors. Try swapping the driver leads at one end in case such is the case.

Good news, with the suggested RS-485 wiring, the Controller is responding to requests. There are checksum errors so more debugging needed. Appreciate the help getting to this far.

John