AlfredoQuintero
Lifetime Supporting Member
Hello:
I have to connect a RS232 Modbus RTU slave that only has Tx, Rx and GND signals to a Modbus RTU master.
However, all RS232 to RS485 converters that I have managed to find only work if the complete set of RS232 signals are present.
Interestingly, while trying a number of things after hours of work, accidentally I wired the following setup and worked!
To double check, I used two different serial boards on the PC (a PCIe one and a USB one) with same results:
Windows PC __________________ | ___ Modbus RTU
MBPOLL ______________________ | ___ (RS232C)
PCIe or USB to RS485 ________ | ___ Slave
Converter _____________________ |
___________________ (Pin 1) A+ <-|-> GND
____________________ (Pin 2) B- <-|-> Rx
__________________ (Pin 5) GND<-|-> Tx
The above setup works, but I cannot figure out why and do not want to recommend the solution to the customer unless I can explain why this works.
Will be grateful for advice on this issue. Thanks.
I have to connect a RS232 Modbus RTU slave that only has Tx, Rx and GND signals to a Modbus RTU master.
However, all RS232 to RS485 converters that I have managed to find only work if the complete set of RS232 signals are present.
Interestingly, while trying a number of things after hours of work, accidentally I wired the following setup and worked!
To double check, I used two different serial boards on the PC (a PCIe one and a USB one) with same results:
Windows PC __________________ | ___ Modbus RTU
MBPOLL ______________________ | ___ (RS232C)
PCIe or USB to RS485 ________ | ___ Slave
Converter _____________________ |
___________________ (Pin 1) A+ <-|-> GND
____________________ (Pin 2) B- <-|-> Rx
__________________ (Pin 5) GND<-|-> Tx
The above setup works, but I cannot figure out why and do not want to recommend the solution to the customer unless I can explain why this works.
Will be grateful for advice on this issue. Thanks.
Last edited: