Appendix 1 Modbus Protocol
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TI 01W01A56-01EN
Appendix 1 Modbus Protocol
Overview
Gateway provides Modbus/TCP server (slave) function. During Modbus communication, the
Field Wireless Device data is transmitted to the host system. Below are supported Modbus func-
tion codes.
• Read Input Register (3X)
Modbus Function Code: 0x04, Address: 0~ 66535
• Write Holding Register (4X)
Modbus Function Code: 0x10, Address: 0~66535
Before transmitting data to a host system, it is necessary to map the transmission process value,
device status, alert information and other data on registers.
In the host systems, system engineering is required to embed the error detection mechanism us-
ing Device Status of each wireless system component, Process Data Status, and self-diagnosis
status (DIAG_STATUS) of the field wireless device; error types can be identified.
NOTE
Process Value will hold previous value if the Communication error or Sensor error occurred.
Therefore you need to check the Process Data Status in order to confirm the data quality.
Parameters
[PV]
Below is the Process Value data block. Data block always starts with 8bit “Data Status” informa-
tion.
Data Status
(8bit :Unsigned16)
Value
(32bit: Float)
The Modbus registers are all 2 bytes (1 word). Therefore, PV is mapped as below with 8bit re-
served space.
16
8 7
0
00000000
Data Status (8bit)
Value (Upper 16bit)
Value (Lower 16bit)
Mar. 31, 2014-00