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7.2
Commissioning
If an error is detected in the received request an exception frame is returned.
| - MBAP Header - | - Function Code - | - Exception code - |
The returned function code, in case of an exception, is the transmitted function code
with bit 7 set (that means that 0x03 Î 0x83, and 0x10 Î 0x90).
Exception codes
0x01
Function code not supported
0x02
Not allowed register no.
0x03
Too many registers or uneven no. of registers, as every register in motor/module is 32 bit
and requires 2 x 16 bit modbus registers.
(0x03) Read Holding Registers
Read of registers. Max. 124 x 16bit registers at a time (=62 x 32bit registers). Only even
no. of 16bit registers is supported. The response time is increased slightly for every register added. See Minimum poll time, page 149 for minimum poll time.
Request:
7 bytes
1 byte
2 bytes
MBAP header
Modbus Cmd.
(0x03)
Motor register no. x 2 or module
Register count
register no. x 2 + 0x8000
2 bytes
Response:
7 bytes
1 byte
1 byte
2 bytes
MBAP header Modbus Cmd. (0x03) Data byte count Register value low 16bit
2 bytes
Register value high 16bit
Example, read of module register 3 (= IP address = 192.168.100.1 =
0xC0.0xA8.0x64.0x01):
Request |0x00|0x01|0x00|0x00|0x00|0x06|0x01|0x03|0x80|0x06|0x00|0x02|
Response – (Note the byte order!)
|0x00|0x01|0x00|0x00|0x00|0x07|0x01|0x03|0x04|0x64|0x01|0xC0|0xA8|
Possibly exception responses: 0x02, 0x03.
For further documentation see “Modbus_Application_Protocol_V1_1b.pdf” and
“Modbus_Messaging_Implementation_Guide_V1_0b.pdf” found on www.modbus.org.
!
148
Please notice: Even though all registers is transmitted as 32 bit, some of them
originally derive from 16 bit in the case of MAC050-141. In those situations it
is necessary to interpret them as 16 bit to get the sign correct.
JVL Industri Elektronik A/S - User Manual - Ethernet expansion modules for MAC motors