I just received a PR55-17C RS-485 Modem & PR55-44 RTD Sensor for testing. I will be connecting these to a PLC so I have a USB->RS-485 Adapter installed on my PC.
I can run HTerm at 9600,8,1,N and communicate with the modem. When I press the reset button on the PR55-44, I get a string back in HTerm.
Using the latest version of Alpha Station, I am unable to communicate with the modem. I have Alpha Station configured with the same serial COM port and baud as HTerm. When I click on ‘Sensor View & Setup’, I receive the error “Unable to communicate with Modem”. Even though communications work with HTerm, I ran the Communications Recovery options and still receive the same error. HTerm is shut down before running Alpha Station and I have lights blinking on my RS-485 Adapter like Alpha Station is attempting to connect to the modem.
Is Alpha Station compatible with the PR55-17C or do I need to be using the older Labview Utility?
I just noticed another problem. The string I am receiving in HTerm is the correct length (PR55-44 Run Mode = 29 bytes) but the start delimiter is wrong. It should always be 0x7E but I am receiving 0xA0 from the modem.
Put the modem in configuration mode and sent a 0xF5 and a 0xF6 to read the port speeds. No response from the modem.
Connected HTerm to my Test PLC using my USB->RS-485 Adapter and sent a string of data which mimics the string that should be sent by PR55-44 / PR55-17C. So my problem doesn’t look like an issue with my PC / HTerm / USB Adapter config.
do you have the standard version of PR55-17C ?
it has 3 jumpers. 1,2,3 . all 3 are set ?
Issue resolved. It comes down to your definition of A & B. My USB->RS-485 Adapter and PLC gear are marked + & -. PR55-17C is marked A & B. A quick Internet search will return A = - and B = +. Apparently there is quite a bit of confusion if you dig a little deeper and search for A/B vs +/-. This search reveals that the TIA/EIA definition and the chip maker’s definition are different.
So the bottom line is I had to swap wires so my + is on your A and my - is on your B.
What is also interesting is the strange string I was receiving from the Modem with the incorrect start delimiter. I assumed if the wires were reversed then there would be no communications between my PC and the Modem. This is incorrect. In fact, the bits are inverted producing the strange string.
glad you figured it out.
i am not sure how it had any communication with old setup. in the old setup did it only add one extra byte in the starting and rest were correct ?
or all were incorrect and only thing correct was the number of byte+ one extra byte ?
I am NOT an EE, but I saw this forum post and that prompted me to swap wires:
As far as the string returned, the length was correct (29 bytes - no extra byte) but it looked jumbled. With the wires swapped, the Start Delimiter is always A0 instead of 7E. There must be some EXOR that explains the change in binary the results in A0 from 7E.