We have a ModBus device communicating with a PC COM port. The device is a 2-wired RS485 and converted to RS232. We want to get rid of that PC and use a Digi One to bring the RS232 to the network.
Right now we can see the COM port created by RealPort on the network, but unable to talk to the divice.
Is the serial port on Digi One a DTE just like a PC COM port? Does it provide port Power?
If I skip the 485/232 conversion, which pins on the RJ45 serial port of Digi One should I connect the 2 RS485 wires (Tx(A) and Tx(B))?
Yes, the Digi ports are DTE, the same as the serial port of a PC.
The Digi ports are not designed to supply power to the connected device.
If you need to supply power to the connected converter, then you may have to change to the PortServer TS1 P MEI (the “P” is for the “powered” modules).
Below is a link to the product data sheet. Pin 1 can supply 5 volts up to 200 mA. Pin 9 can supply 9 volts yo to 100mA.
For details please see this link: http://www.digi.com/pdf/prd_ds_portservertspmei.pdf
For using 2-wire rs485, 10 pin rj45, pin 2 is Data- B) and pin 6 is Data+ (A). If you are using 8 pin rj45 connectors, the pin #s are 1 and 5 respectively.
Details are in the Command Reference manual at this link on page 212: http://ftp1.digi.com/support/documentation/92000304_N.pdf
It is usually good to also use the signal ground wire as well (pin 7 for 10 pin rj45s, pin 6 for 8 pin rj45s).
Thank you for the information. The problem has been solved but there’s something I don’t understand.
I used a straight RJ45-DB9 cable to connect the Digi port to our device, it didn’t work. It worked when I used a crossover RJ45-DB9, a crossover DB9-DB9, and a straigh DB9-DB9 together. My understanding is, 2 crossovers and a straight should be equivelent to a straight. How come a single straight doesn’t work?
It may have to do with control signals. You’d have to trace the path of each signal in the crossover/crossover/straight configuration with having it just straight to see for sure.