Hi all, hope somebody can help.

I try to get the DI state over an USB-RS485 Adapter from a modbus device.

I have to send "01 02 00 00 00 06 CRC" over COM4 -> USB-RS485 Adapter to the modbus device.

I decided to try this with openapc to have a sophisticated GUI.

So, i setup an Modbus RTU Master in Flow Editor

Then i started the project and i can see on COM4 "01 02 00 00 00 20 79 D2" is send, that may be correct.

I can change the first byte by changing the "IO0 Slave Adress" in Openapc Modbus Definition.

I can change the second byte by changing the "IO0 Modus" in OPenapc Modbus Definition.

I can change the third and fourth byte by changing the "IO0 Offset" in OPenapc Modbus Definition.

So far, so good.

But which parameter in the Modbus Definition is changing the fifth and sixth byte to a value "00 06" ???

Hope somebody can help me.

I did the same with modpoll succesfull and get this result

------------

...win32>modpoll -m rtu -a 1 -r 1 -c 6 -t 1 -1 -b 9600 -d 8 -p none com4

modpoll 3.4 - FieldTalk(tm) Modbus(R) Master Simulator
Copyright (c) 2002-2013 proconX Pty Ltd
Visit http://www.modbusdriver.com for Modbus libraries and tools.

Protocol configuration: Modbus RTU
Slave configuration...: address = 1, start reference = 1, count = 6
Communication.........: com4, 9600, 8, 1, none, t/o 1.00 s, poll rate 1000 ms
Data type.............: discrete input

-- Polling slave...
[1]: 0
[2]: 0
[3]: 0
[4]: 0
[5]: 0
[6]: 0

----------------

While monitoring COM4 i saw that "01 02 00 00 00 06 F8 08" is
send.

Thanks

roman