compact RIO, 4 Port RS-232 Module 9870, continous write and read on all 4 Ports

[PietH]

I use compactRIO 9012 controller with the 4 slot cRIO-9111 chassis.

Modules:

9870 4 RS-232 ports

9205 analog in module

I try to acquire in parallel data from 4 RS-232 devices and 8 analog channels from voltage sources.

Starting point was the code example "NI 9870 - Continuous Serial Read - On-Demand Write" (https://forums.ni.com/t5/Example-Code/NI-9870-Continuous-Serial-Read-On-Demand-Write/ta-p/3996157). I have added some code for analog data reading, and it works.

With simple RS-232 devices (i.e sending only one poll and than read) it was no problem to share one DMA with all 4 ports to read and write data between FPGA and RT.

If I try to acquire data from devices which uses much more complicated RS-232 protocols (different read and write commands, real-time data up to 500 Hz and so forth...), it was not possible to read all data even from only two devices. The vi run into a lot of timing problems. If I could use one DMA for each RS-232 port it was no problem, but this is not possible.

Has anyone experiences with compactRIO and the 9870 module? How many DMA´s are possible?

Thanks a lot in advance

Peter

[Manuel_A.]

Hi PietH,

i read about a similar Problem where someone acquired data over a 9870 Module and was missing data. He could solve his Problem by increasing the timeout on the DMA to 100. Maybe this helps you.

Kind Regards,

Manuel