Are RS232 and RS485 the same signal AFTER converted to USB? Cant get 2-way communication.

Thread Starter

no_code

Joined Feb 3, 2021
6
I have a stepper motor that I am trying to control with an Epson robot. I can get the robot program to give the stepper string commands using the PC's COM port (and it responds as expected) but I cannot figure out how to receive messages from the motor. The stepper is RS458. I have an RS485 to USB converter to the PC. The Epson software, however, only lets me configure a COM port as an RS232 port. Does the protocol matter once it is converted to USB?
Is R232 > USB > RS485 possible or is that my problem?
I am pretty new to automation and communications.
 

dendad

Joined Feb 20, 2016
3,906
RS232 and RS485 are basically defined voltage levels and each can carry various protocols.
You may need to find out what the protocol is first.
Is the RS485 full or half duplex?
Is it packets of data like ModBus or just straight ASCII text?
Can you post details of the devices as without that, it is really hard to help.
If your PC has a com port, why are you worrying about USB, or is it a virtual com port?
Details please.
 

Thread Starter

no_code

Joined Feb 3, 2021
6
RS232 and RS485 are basically defined voltage levels and each can carry various protocols.
You may need to find out what the protocol is first.
Is the RS485 full or half duplex?
Is it packets of data like ModBus or just straight ASCII text?
Can you post details of the devices as without that, it is really hard to help.
If your PC has a com port, why are you worrying about USB, or is it a virtual com port?
Details please.
First, I appreciate the reply. Also, apologies for my ignorance.
RS485 is full duplex I think- that is 4 wire, right? Motor configuration allows me to pick. I have full checked. It has 4 wires and a ground.
Packets are ASCII text.
I guess the port is virtual- from the driver.
All the stepper components are Automation Direct.
motor and drive- STP-MTRD-23042RE
adapter- STP-USB485-4W
 

Thread Starter

no_code

Joined Feb 3, 2021
6
Jumpers in the STP-USB485-4W ? Factory settings. Product literature said jumper settings should be optimal. Is it possible to get 1-way communication if I have a protocol "mix-up"?
 

MrChips

Joined Oct 2, 2009
24,143
You are being confused with RS-232, RS-485, USB and COM ports.
At the hardware level, RS-232 and RS-485 are voltage levels and tells you nothing about full-duplex vs half-duplex.

A PC COM port is basically a legacy serial UART interface and it can be RS-232, RS-485, TTL, or any HW voltage level that you choose.

COM ports and USB are really two different almost incompatible serial protocols. A USB-to-UART bridge is actually a kludge to make a very complex protocol (USB) emulate a UART serial full-duplex interface.

So it depends on the HW interface on your device. Is it serial TTL, RS-232 or RS-485?
In order to connect your PC USB to the device, you need a USB-to-serial cable and you can specify the serial end of the cable, i.e. TTL, RS-232 or RS-485. Failing that you can go with a USB-to-TTL serial bridge and then convert from TTL to the desired HW interface.
 

Thread Starter

no_code

Joined Feb 3, 2021
6
You are being confused with RS-232, RS-485, USB and COM ports.
At the hardware level, RS-232 and RS-485 are voltage levels and tells you nothing about full-duplex vs half-duplex.

A PC COM port is basically a legacy serial UART interface and it can be RS-232, RS-485, TTL, or any HW voltage level that you choose.

COM ports and USB are really two different almost incompatible serial protocols. A USB-to-UART bridge is actually a kludge to make a very complex protocol (USB) emulate a UART serial full-duplex interface.

So it depends on the HW interface on your device. Is it serial TTL, RS-232 or RS-485?
In order to connect your PC USB to the device, you need a USB-to-serial cable and you can specify the serial end of the cable, i.e. TTL, RS-232 or RS-485. Failing that you can go with a USB-to-TTL serial bridge and then convert from TTL to the desired HW interface.
Again, thank you for your reply. You gave me plenty of reading to do. I am only beginning to scratch the surface when it comes to automation communication setups.
I wanted to let you know that I was able to solve my issue. The problem was that my port on the robot was configured wrong. I set the termination characters from "CRLF" to just "CR" and now it works like a charm. I was initially concerned that what I was trying to do was not possible but thanks to your input, I understand a little more about what I am working with . Thank you.
 
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