SCT Weight Transmitter – 20 Series Technical Manual
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Modbus Supported Functions
Among the commands available in the MODBUS-RTU protocol, only the commands in
are used to manage
communication with the instruments. Other commands may not be interpreted correctly and could generate errors or system
shut-downs:
The interrogation frequency is linked with the preset communication rate (the SCT20-MB will stand by for at least 3 bytes before
beginning to calculate a possible response to the query). The
?parameter (
) allows for a further
delay in the instrument response, and this directly influences the number of possible queries in the unit of time.
For additional information on this protocol, refer to the general technical specification PI_MBUS_300. In general, the query and
response to and from a source instrument are organized as follows.
Function 3: Read Holding Registers (Programmable Register Reading)
Table 3-27. Programmable Register Reading (Modbus-RTU)
Query
Address
Function
Add. Reg. 1
No. register
2 bytes
A
0x03
0x0000
0x0002
CRC
Tot. bytes = 8
Tot. bytes = 3+2*No. re2
in which:
No. registers= number of Modbus register to be read, starting from the Address 1° register
No. bytes = number of data bytes to follow
Function 16: Preset Multiple Registers (Multiple Register Writing)
Table 3-29. Multiple Register Writing Query (Modbus-RTU)
QUERY
Address
Function Add. reg. 1
No. reg.
No. bytes Val. reg.1 Val. reg.2
2 bytes
A
0x10
0x0000
0x0002
0x04
0x0000
0x0000
CRC
Tot. bytes = 7+2*No. re2
Tot. bytes = 8
Function
Description
03 (0x03)
Read Holding Register (Programmable Register Reading)
16 (0x10)
Preset Multiple Registers (Multiple Register Writing)
Table 3-26. Modbus-RTU Supported Functions
RESPONSE
Address
Function No. bytes Register1 Register 2
2 bytes
A
0x03
0x04
0x0064
0x00C8
CRC
Table 3-28. Programmable Register Reading Response (Modbus-RTU)
RESPONSE
Address
Function
Add. Reg. 1
No. register
2 bytes
A
0x10
0x0000
0x0002
CRC
Table 3-30. Multiple Register Writing Response (Modbus-RTU)
