06-05-2017 05:16 PM
Hello,
do I need a converter if I want to wire RS485 2 wire onto the NI 9871? The NI9871 says its RS485, so I just joined RXD-/TXD- and RXD+/TXD+ and connected it to the - and + on the RS485 output. But in VISA test panel I don't get any read, just timeout. But Query returns 6 bytes for *IDN?\, the open ports get timeout on query
Cheers,
06-06-2017 04:36 PM
Steffen01,
The NI-9871 does support RS485, so a converter should not be necessary. Is there a timeout error code that you can provide? What software version are you using?
Angela L.
National Instruments
06-06-2017 05:17 PM
Hi Angela,
I get these 2 errors. I will just put a terminator resistor in, see if that helps. I read something, on 2 wire more its better, to put them in. Also there was something, connect TXD- to RXD+ and vise versa for 2 wire and then to - and + of the Modbus device
Cheers,
Steffen
06-06-2017 05:17 PM
06-06-2017 05:54 PM
Thanks for the screenshots. I also did some digging through our past discussion forums and found one that was pretty similar. Have you looked through this yet?
NI 9871 wiring to device with A and B terminals
06-06-2017 06:11 PM - edited 06-06-2017 06:12 PM
yes, connected 4 with 8 and 5 with 9, then to + and - of the modbus card, this one.
Put in a 100 Ohm resistor for terminator just then, see if that changes something. Its just 0.5m long cable.
Installed all the drivers on the cRio.
06-06-2017 06:28 PM - edited 06-06-2017 06:30 PM
Modbus uses an RS 485 physical layer. However, it has additional requirements for other layers. Are you using NI-Xnet?
Modbus does not act like SCPI
06-06-2017 06:48 PM - edited 06-06-2017 07:09 PM
its this one wit a modbus card, on 19200 Baud, nothing extra. Fot now just trying to see if I got the wiring right in MAX and VISA test panel.
Slave address is 001, not 01, but that should not make a difference, still just 01 in hex.
Configure Labview as Master, how? Is there options in MAX?
I just got an answer I need this one, a repeater. Or Can I set the 9871 somewhere, this channel is 2 wire, not 4? This only works in Labview, not in MAX? I found some examples there, half duplex.
http://www.bb-elec.com/Learning-Center/All-White-Papers/Serial/4-Wire-to-2-Wire-Connections.aspx
set windows for half duplex:
http://digital.ni.com/public.nsf/allkb/3EB322DAEAACB19D862571F500021C00
06-08-2017 07:56 AM
still no luck, but found this
http://digital.ni.com/public.nsf/allkb/1D516C10D7EDFAC6862571110073B8F4
https://www.ni.com/getting-started/set-up-hardware/instrument-control/drivers
will try tomorrow
suppose I have to set MAX to 2 wire.
atached some visa test, fro each register it returns its nuber times 256 as reading. But at least no timeouts