AO consecutive writing - problem

• From: George Pava <pava_at_cs.ubc.ca>
• Date: Thu, 18 Mar 2004 17:04:23 -0800

Hi all,

I am using Measurement Computing PCI-DAS1602/16 card (cb_pcidas driver),
installed comedi(0.7.66 / 0.7.20), and everything runs correctly with one
exception:
2 consecutive writings to different Analog Output channels (ch0, and ch1)
produce wrong outputs.

Details:
...
//aref = AREF_COMMON;
//aref = AREF_DIFF;
aref = AREF_OTHER;
//aref = AREF_GROUND;
rangeNo=3; //[0-10V]

while ( 1 )
{
 comedi_data_write(device, subdev, 0, rangeNo, aref, 0);      //writes 0V to
AO ch0
 comedi_data_write(device, subdev, 1, rangeNo, aref, 65535);  //writes 10V
to AO ch1
}
...

- This will produce AO0=-4V, AO1=+5V; it should be (AO0=0V, AO1=+10V).
- If I leave only one write command in the loop I will get the right output
for that particular channel.
- If I write the same value to both channels, the output would be correct on
both channels.
- I tried different aref (AREF_GROUND, AREF_DIFF) but same wrong results.


I would appreciate any comments you may have.

Thanks,
George

Received on 2004-03-19Z01:04:23