ICP DAS, MDC-211-ZT user manual , v1.0 Page 39
Copyright © 2018 by ICP DAS. All rights are reserved.
Modbus TCP/RTU Protocol
The users can write data with corresponding function code 05/06/15/16 to the mapping
addresses of MDC
‐
211-ZT Internal Register, and then can control the output channels of the
Modbus RTU Slave devices.
Figure 5.1 Modbus Internal Register table in Web interface
【
Example
】
In Figure 5.1 above, it is assumed that the Modbus slave ID of MDC-211-ZT is
0xAA. At the same time it is also acting the Modbus Master, the command of number #007
controls the DO channel of I/O device (e.g. ZT-2043, 14-ch DO).
Originally, the PC uses the function code 15 to control the Internal Register [00000:00013] of
Modbus RTU device (Modbus ID: 03) directly. When the MDC-211-ZT is added as a modbus
data concentrator, the PC needs to poll the MDC-211-ZT instead. Therefore, the command
needs to be changed according to the corresponding Internal Register table above, to
control the Internal Register [00008:00021] of MDC-211-ZT (Modbus ID: AA). The commands
as shown below:
Original command
03
0F
00 00
00 0E 02 FF 3F + CRC16
New command
AA
0F
00 08
00 0E 02 FF 3F + CRC16