User guide

Communication protocol Serie30 Page 10/37
4.3 Description of MODBUS functions
This section describes the MODBUS functions supported by Series 30 transmitters (device Class.Group = 5.20)
Overview:
F3: Read registers on MODBUS address space
F6: Write single register on MODBUS address space
F8: MODBUS Echo function
F16: Write multiple registers on MODBUS address space
4.4 Modbus Communication Examples
address
request response
received value
250
250 3 0 2 0 2 112 64 250 3 4 63 117 228 166 102 72
0.96052 bar
Read P1
1
1 3 0 2 0 2 101 203 1 3 4 63 117 240 123 227 222
0.960701 bar
Read P2
1
1 3 0 4 0 2 133 202 1 3 4 63 118 6 224 21 213
0.961042 bar
250
250 3 0 8 0 2 80 66 250 3 4 65 181 99 178 29 163
22.6737 °C
Read
TOB1
1
1 3 0 8 0 2 69 201 1 3 4 65 181 192 121 110 11
22.719 °C
Read P1
and
TOB1
1
1 3 1 0 0 4 69 245 1 3 8 63 117 227 210 65 182
28 32 160 119
0.960508 bar
22.7637 °C
Purple = MODBUS register address
4.5 Function 3: MODBUS Register Read
Read a number of subsequent registers in the MODBUS address space starting with StAdd. Note, that the data returned has to
be interpreted according the definitions in “4.9 MODBUS Register Map”.
• Function is implemented in devices Class.Group-Version = 5.20-2.40 and later
• The number of registers read in one cycle is limited:
4 registers for devices Class.Group-Version = 5.20-10.XX and later
2 registers for earlier versions than Class.Group-Version = 5.20-10.XX
• Byte-count of the answer will be an even number (1 register = 2 bytes)
• Addresses that are part of double sized registers, return 0x0000 if only one register is requested
• Returns NaN or Exception 4 in case of a channel error, depending on accessing a “float” or “integer” address.
Request:
DevAddr 0x03 StAdd H StAdd L # Reg H # Reg L CRC16_L CRC16_H
Response:
DevAddr 0x03 # Bytes Data H Data L … Data L CRC16_L CRC16_H
Error:
DevAddr 0x83 Error CRC16_L CRC16_H
Error codes:
2 Illegal data address:
- Wrong starting-address or wrong number of registers
- Start-address not defined, register exceeding defined range return 0x0000
3 Illegal data value:
- Quantity of requested registers out of bound
- Must be <= 4 for devices Class.Group-Version = 5.20-10.XXand later
- Must be <= 2 for devices Class.Group-Version = 5.20-2.40 - 5.20-10.XX
4 Slave Device Failure:
- Value not valid (=> check status)
- Over/Underflow when requesting value as int
- Channel not active and requesting value as int