Digital I/O port of the DAQCard-AO-2DC

Question

I've been trying to write a LabVIEW program to control a t6963c LCD
controller using DAQCard-AO-2DC. I need one 8-bit bidirectional data
port and 6 bits output lines for control signals. Therefore, I set
port A (PA) of the DAQCard as bidirectional data bus, and port B (PB)
as output for control lines.
An example write/read operation of the ports (O,C: write,I: read) is,
PA: O1 O2 I1 O3 O4 I2 ...
PB: C1 C1 C2 C3 C3 C4 ...
The problem is that if I use port_config, port_write, port_read VI's,
there is confliction in PA (Error code -10612, badLineDirError). I
could only read from PA, but could not write. The output of PA is
always 0. I found some statement from
http://www.cvs.rochester.edu/people/b_singer/IOCard/, sayi
ng
"When Other Digital Ports Might Be Reset
Nearly all cards with multiple digital ports use the Intel 8255 chip,
used in PC parallel ports. When you read from a port for the first
time, or after having used it to write, any other port outputs will be
reset. An easy way to avoid this problem is to use a given port for
either reading or writing, but not both, and to do your first read
before your first write."
DAQCard-AO-2DC uses 8255. Does it mean that we cannot use it as a
bidirectional port? How to understand this statement?
My questions are:
1. First of all, is it viable to use DAQCard-Ao-2DC to reach the
target?
2. Can I use port_config/read/write to program?
3. Is there a way to make the output PA and PB change at the same
time? I used dio_read/write. PA, PB changed one after another and the
speed was too slow (one operation takes ~ms).
Thanks.
Dexter

Answer 1

Yes, this is the behavior of the digital lines on the DAQCard-AO-2DC since it does use the Intel 8255 chip. Any time any port is reconfigured, all lines on all ports are reset. There is some information about the the AO-2DC's digital lines on Page 4-5 of the user manual.
http://digital.ni.com/manuals.nsf/webAdvsearch/4F17D424F3411E8B8625665E0065CDB8?OpenDocument
You'll probably find more on the 8255's data sheet. There's one inside the PCI-DIO-24 User Manual. By the way, you can search for manuals online at:
http://www.ni.com/documents/
Each 8255 port can only be configured for either all input or output at any given time. So this is obviously the main problem for you since you have both input lines and output lines on PA.
So, no, I can't t
hink of a great way to get the DAQCard-AO-2DC to work for this application. The PCI-DIO-24/96 cards also use the 8255, but on them you have access to port C where on the AO-2DC you do not. So this probably would work for you.
If you used a 653x device, you could group all your ouput lines into one port. Then you would be able to have all output lines change at the same time.
Hope this helps!
Russell
Applications Engineer
National Intruments
http://www.ni.com/support