Illegal modbus response from serial card

[K C]

The terminators I talk about are at the RS-485 interface NOT at the RS-232.

So the active terminator should be places inside the RS-232-485 converter.

But your problem is the change of the RS-232 interface. So....

But do check the active terminator at the RS-232-485 converter side. Changing the RS-232 interface can be of influence on the ground level of the RS-232-485 converter.

A active terminator are 3 resistor in series connected between Vcc and ground. From Vcc to ground it is 390Ohm + 150Ohm + 390Ohm. The 485 lines are connected across the 150Ohm. A(+) on the Vcc side.

[azwhoony]

To be more accurate, here's the result of my testing. I'm out of idea.

Testing Result	Meter		IO Board
	Converter A	Converter B	Converter A	Converter B
On Board COM Port	-O.K-	-O.K-	Time Out and Illegal Response	-O.K-
PCI Extended COM Port	-O.K-	Illegal Response	Time Out and Illegal Response	Time Out and Illegal Response

 

[azwhoony]

OK KC. I got that. I'll check at the converter side or probably check with the both converter supplier (because I think it's under warranty). Thanks for the hint. Keeps my hopes high again. hehe..

[K C]

OK, I will think about it and see if there is something else I can come up with.

Meanwhile I have my own troubles with a UM232 (USB) to RS-485 converter. I get two extra null bytes before the data but not always. No idea where they are coming from....

Bad time of the year for RS-485 data transfer I think