Sensor Electronics SEC 3000, Instruction And Operation Manual

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SEC 3120 16-bit Modbus Manual Page 25 Of 46 Sensor Electronics Corporation
For Version 1.2 and above December 2012 P/N 1580282, Rev. 1, 20121228
Implemented Functions and Registers Defined
The function code identifies the command being issued to the device. It is one
byte in length and has a value of 1, 3, 5, 6, 15 or 16.
Table 6: Function Codes Supported By SEC 3120
Function Code Description
1
Read Coil Status Registers (not supported)
3
Read Holding Registers
5
Force Single Coil Register (not supported)
6
Preset Single Holding Register
15
Force Multiple Coil Registers (not supported)
16
Preset Multiple Holding Registers
For the current 16-bit version, registers are only mapped for function codes 3, 6,
and 16. Otherwise an exception response will be generated.
In most cases, there is no response for a query that contains an invalid slave
address, invalid CRC data or a non-supported broadcast mode, etc. In some cases, the
unit might issue an Exception 2 as an error response if an invalid register address is
requested for a valid function code. However, if invalid function code is issued, such as
function 07 were transmitted, then an Exception 1 message would be generated to
indicate that the function code is not supported.
Query Coil Status Message
Field Name Example (Hex)
Slave Address 01
Function Code 03
Address High 01
Address Low 5B
Num Points High 00
Num Points Low 03
CRC Low Byte 75
CRC High Byte E4
Response Exception 2
Field Name Example (Hex)
Slave Address 01
Function Code 83
Exception Code 02
CRC Low Byte C0
CRC High Byte F1