Modbus TCP Packet Data

Ignition
1

Hi,
I have this data from master computer commining over ethernet cable:
00 03 00 80 00 01 84 33

Is there anyone there to describe details of the above stream?

Thanks

2

Looks like:

00      unit/slave id
03      function code (Read Holding Registers)
00 80   address (128 decimal)
00 01   quantity (1 decimal)
84 33   checksum

and despite coming over ethernet it looks like it’s just an RTU frame. There’s no MBAP header as there should be on ethernet.

3

Thank you for your reply. This is the type of data as shown on the Modbus 32 simulator However having used another simulation software called Modbus poll and the data is more detailed with extra info i.e. header as following:
00 00 00 06 00 03 00 08 00 01 84 33

Any suggestion? in particular would you agree that the unit ID = ‘0’

4

I don’t know what the extra data is in those bytes. The MBAP header for TCP is 7 bytes.