CM-2201/CM-2202
Communications
©2018 Nelson Heat Tracing Systems
www.nelsonheaters.com
GA2497 Rev.6
15
8.0 Communications
The Nelson Heat Trace CM-2201 supports a subset of the Modbus
®
RTU protocol format that provides monitoring,
programming, and control functions using Read (03) and Write (05-06) register commands.
General Information
Serial Port:
Select the serial port that corresponds to your RS-485 adapter.
USB to Serial adapter may be used for devices without serial connections.
Baud Rate:
User Defined at 2400, 4800, 9600 or 19200
Data Bits:
8
Stop Bits:
1
Parity:
None
Device Address:
User Defined between 1 and 255
Modbus Registers
For all Modbus register addresses, see Appendix E.
Example of checking alarms via Modbus from a remote
terminal.
Controller SETTINGS and Status used on this example:
a.
Modbus address 04
b.
Baud rate 19200; non-parity; Stop bit 1.
c.
High Temperature alarm active
1.
To check if any alarm is activated, send the
following instruction:
04 03 0046 0026 2590
04 = controller Modbus number
03 = Modbus function code 3
0046 = start reading from data address
70
0026 = the next 38 addresses
2590 = CRC
2.
The controller will answer with value 0x02 (High
Temperature Alarm) active Alarm
3.
Once the alarm condition has been resolved, the
alarm can be cleared by sending the following
instruction: “04 05 0045 FF00 9C4C”
04 =controller Modbus number
05 = Modbus function code 5
0045 = writing to data address 165
FF00 = erase command
9C4C = CRC
At this point the controller enters the alarm into
the alarm log memory and clears the active
alarm. To check the alarm log memory, see
below.
4.
If the command to check if any alarm is
activated (as shown in (1) above) is now sent to
the controller, and assuming no other alarms
have since been activated, the controller will
answer with 0x0000 (no active alarms).
5.
To check the alarm log memory, issue the
following instructions:
04 03 006E 0026 A598
04 = controller Modbus number
03 = Modbus function code 3
006E = start reading from data address
110
0026 = the next 38 addresses
A598 = CRC
6.
The High Temperature Alarm will be listed
here, so the controller will answer 0x02. The
Alarm log can hold 20 alarms. After 20 alarms
the oldest alarm will be erased to allow for
storage of the new alarm. To erase all alarms on
alarm log, see below.
7.
To erase all alarms on the Alarm log from the
remote terminal, send the following instruction:
04 05 0097 FF00 3D83
04 = controller Modbus number
05 = Modbus function code
0097 = data address 151 to write
FF00 = command to erase all memory log
3D83 = CRC
Note: The DPC can read up to 45 addresses per command
