Sierra 241-VTP, 240-VTP instruction manual An attempt to read registers that don’t exist

Appendix E MODBUS Commands Series 24-HP Instruction Manual

A typical response from the device is as follows: *note these are the older register definitions

01 04 18 00 00 03 E8 00 00 7A 02 6C 62 00 00 41 BA 87 F2 3E BF FC 6F 42 12 EC 8B 4D D1

01 Device address

04 Function code

18 Number of data bytes = 24

00 00 03 E8 Serial number = 1000 (unsigned long)

00 00 7A 02 Totalizer = 31234 lbm (unsigned long)

6C 62 00 00 Totalizer units = “lb” (string, unused characters are 0)

41 BA 87 F2 Mass flow rate = 23.3164 lbm/sec (float)

3

3E BF FC 6F Volume flow rate = 0.3750 ft /sec (float)

42 12 EC 8B Pressure = 36.731 psia (float)

4D D1 CRC

An attempt to read register(s) that don’t exist

01 04 00 00 00 50 F1 D2

01 Device address

04 Function code 4 = read input register

00 00 Starting address

00 50 Number of registers = 80

F0 36 CRC

results in an error response as follows:

01 84 02 C2 C1

01 Device address

84 Function code with most significant bit set indicates error response

02 Exception code 2 = invalid data address

C2 C1 CRC

Request the state all three alarms:

01 02 00 00 00 03 38 0B

01 Device address

02 Function code 2 = read discrete inputs

00 00 Starting address

00 03 Number of inputs = 3

38 0B CRC

and the unit responds with:

01 02 01 02 20 49

01 Device address

02 Function code

01 Number of data bytes = 1

02 Alarm #2 on, alarms #1 and #3 off

20 49 CRC

To reset the totalizer:

01 05 00 00 FF 00 8C 3A

E-8 IM-24-HP