User Guide
Supported Modbus Functions
The Modbus functions that are supported by the A90 are as follows:
Decimal Hex Description
01 0x01 Read Coils
02 0x02 Read Discrete Inputs
03 0x03 Read Holding Registers
04 0x04 Read Input Registers
05 0x05 Write Single Coil
06 0x06 Write Single Register
08 0x08 Diagnostics (Partly Supported)
15 0x0F Write Multiple Coils
16 0x10 Write Multiple Registers
43 0x2B Read Device Identification (Partly Supported)
Diagnostics (Function Code 0x08)
All of the following diagnostic sub-functions are supported except sub-function 0x03 (This is only required for
ASCII protocol. A request on this subfunction generates an ILLEGAL DATA VALUE exception.)
Sub-Function Code Description
Decimal Hex
00 0x00 Return Query Data
01 0x01 Restart Communications Option
02 0x02 Return Diagnostic Registers
03 0x03 Change ASCII Input Delimiter (Unsupported)
04 0x04 Force Listen Only Mode
05...09 0x05...0x09 Reserved
10 0x0A Clear Counters and Diagnostic Register
11 0x0B Return Bus Message Count
12 0x0C Return Bus Communication Error Count
13 0x0D Return Bus Exception Error Count
14 0x0E Return Server Message Count
15 0x0F Return Server No Response Count
16 0x10 Return Server NAK Count
17 0x11 Return Server Busy Count
18 0x12 Return Bus Character Overrun Count
19 0x13 Reserved
20 0x14 Clear Overrun Counter and Flag
21...65535 0xnn Reserved
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