MODBUS TCP help

mehmet karakaya Guest 2018-08-29 14:39 #5539170

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hello dear forum,

I am trying to MODBUS TCP comunicate STM32 with Mach3

I have read the TCP documents in internet and learned
that first of all Mach3 send a TCP SYN message to the STM32

this time I send a SYN-ACK message to Mach3

after this Mach3 must send a ACK message to STM32

as you can see in the attached picture

the SYN from Mach3 and SYN-ACK from STM32 is there
(192.168.1.2) PC (192.168.1.110) STM32

however ACK from Mach3 is missing and Mach3 reports "conection timeout"

there is a warning from Wireshark yellow coloured

what does this warning say ? what shall I do next ?

thank you

Attached files:

wireshark.JPG (200 KB)

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Moddy Guest 2018-08-29 14:42 #5539174

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The error means there's an acknowlede that's not corresponding to a 
message sent / received before. Thus the ack cannot be interpreted. 
Probably that's the reason why your modbos won't work.

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mehmet karakaya Guest 2018-09-08 09:40 #5549665

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hello dear forum,

I finally managed to respond to Mach3 MODBUS TCP SYN message

I have sent a correct SYN ACK message back to Mach3

but this time Mach3 responds with RST message - see picture

what shall I send back to Mach3 in order to finish connection process

thank you

Attached files:

wireshark2.JPG (210 KB)

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