Real-Time Measurement and Control

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Setting up 2-wire RS-485 communication on a cRIO-9068 base COM port

I have a similar post in the Instrument Control board outlining this problem, but I want to be more specific on the cRIO side of the issue as I think the problem may pertain to the configuration of the port, which would be a CRIO-specific function. I am attempting to create a communication link between a cRIO-9068's onboard (COM3) RS-485 port and a slave flow meter device, an Endress+Hauser Coriolis meter, which I've validated through a separate diagnostic tool as having Slave address 247 / 19200 / even parity. My development system is LV2K15 SP1 on Win7Pro SP1. 


I have configured a few MODBus slave devices in the past with the cRIO-9068, and I can't seem to get this one working with the usual run-through. This is my first time utilizing COM3, the on-board serial port designated as RS-485. I am using I/O Server to create a MB.lvlib library that I use to create a range of 300000/400000-series addresses to read from. I then deploy this to my CompactRIO controller (Scan Mode configuration). The only thing I can get to seemingly indicate new values or change noticeably in realtime are the CommFail boolean (always on) and the Updating boolean (intermittent on/off). 


I have consulted this link on setting up 2-Wire (Half-Duplex) communications with the RS-485 port and am complying with it.

I have consulted this link on RS485 termination, and am using a 109-ohm termination resistor on each end, though it is not a multi-node drop bus, just end to end. 


My specific question/confusion seems to be in how change the serial port configuration to an explicit 2-wire mode. I don't see the option anywhere in MAX. For my 9068, I don't see the advanced tabs within MAX and it's always greyed out with random serial settings and says it can't be accessed. Does having the MB.lvlib deployed to the project automatically grey this out and tell MAX that is has programmatic control? I know you can programmatically modify this via a property node setting (also shown on previous link) but when I do this in the program, it cannot "gain access to the resource" as if it's in use. All of my error outputs are code -1967353902 very similar to this user's issue but I've deleted the other Shared Variable + ModBUS library I used in the project. 


TLDR: Using cRIO-9068 + I/O Server for RS-485 based MODBus connection to a slave. Can't configure it to 2-wire mode in the I/O Server settings. Need to use VISA object property nodes? If so, how?



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