Problem with digital I/O port of a DAQ card

[dexter]

Hi,

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/, saying

"W
hen 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).

I appreciate your help.

Dexter

[Dennis_Knutson]

With digital I/O using the 8255, you cannot configure individual line direction. All pins of a single port must be either input or output. You'll need to find another DAQ card. I believe that the E series devices have digital I/O programmable on a line basis.

[Filipe A.]

Hello;

You can set certain ports to be bidirectional. Note that these are ports from the 8255 chip. Double check on the DAQ device Users Manual what ports can be set as bidirectional mode.

There are other boards I would recommend that allow you to configure bidirectional operations, such as the DIO-24 and the DIO-96.

Perhaps you actually want individually configurable lines in a port, which the 8255 chip does not allow. In that case, the PCI-6025E does allow you to choose some lines as input and some as output in the same port. That would be calling the Dig_Line_Config functions for the appropriate lines.

Hope this helps.
Filipe A.
Applications Engineer
National Instruments

[dexterchn]

hi Filipe,

Thanks for the answer.

Acutally, I want to set port A to be bidirectional bus. For DIO-24, port A can be set as such in Mode 2. However, I don't see in the manual of DAQCard-AO-2DC saying any word about bidirectional bus, although it says that PA and PB are "bidirectional digital data lines". The ports in AO-2DC can be set as either input or output. But cannot be programmed to be working in mode 2.

So my guess is that, for AO-2DC I have to reconfigure the port A whenever the direction of the data flow is changed but that will reset the port B. I'm afraid my initial thought won't be relized by using AO-2DC.

Regards,

Dexter

[dexter]

Thanks, Dennis.

What I want to configure is the port, not individual line. I tried to
use Port Write / Port Read to make the port A bidirectional. However,
I found that Port Read only read back what Port Write has written.
Therefore, I cannot read data from outside the DAQ card.

Is there a way to configure the port as bidirectional?

Dennis Knutson wrote in message news:<50650000000500000091A00000-1031838699000@exchange.ni.com>...
> With digital I/O using the 8255, you cannot configure individual line
> direction. All pins of a single port must be either input or output.
> You'll need to find another DAQ card. I believe that the E series
> devices have digital I/O programmable on a line basis.

[ozimmer]

Dexter,

An article from knowledge base ("understanding bi-directional mode on 8255 chip") seems to enlighten your problem, which is mine too, 1 year later 🙂

Did you succeed in doing what you were trying to do ?

I understand that STB and ACK lines should be driven externally to trigger input to or from port A to the PC buffer. DIG_In_Port and DIG_Out_Port are used on PC side to load/read the buffer. Is that right ?

Any other precisions about 8255 port A bidirectional operation ? oz