NAT9914 error, DAV signal

[hdx]

Hi!

I have a error in my NAT9914 on the GPIB inteface, I wrote about this before and I get a proposal to use a GPIB analyzer,
I didnt have one but I used a logic analyzer, and I think that the problem have been found,
but I dont know how to solve it. Here is the error.

I can send data messages without any problem. I can also receive one data message from a instrument.
But after I received data to the NAT everything just stops working propelly, both the sending and the receiving parts.

The logic analyzer shows that the DAV line in the NAT is asserted two times on the same byte, the instrument will get the same

byte two times. This is only happening after I received someting, before that the NAT sends it correctly.

I would b
e very thankful if I could get same help with this problem.

RH

[DiegoF]

Hi,

There's a couple of things I find confusing.

You say the problem occurs when the NAT9914 is receiving data, and that the DAV line is asserted two times. If the NAT9914 is receiving, the DAV line is driven by the talker, not the 9914. It's not clear to me who's talking and who's listening.

Also, What is the state of the other handshaking lines?

DiegoF.
National Instruments.

[hdx]

Hi!

I will try to explain this better.

Now for example:

I sends:
conf:freq => the instrument receives it
conf:volt:ac => the instrument receives it
*rst => the instrument receives it
*idn? => the instrument receives it and returns the information

Now when I have done this I will send the "conf:freq" again. Now the instrument says
-113 unrecognized command(or something like that).

When I analyze this in a logic analyzer it sems that the NAT asserts the DAV line 2 times on every single byte I send.

I also noticed today that the T1 delay is only 200 ns when the NAT does not work. When its working it is 7 us.

[DiegoF]

Hi,

My confusion lies on what is the NAT9914 doing in this system. Is it in the instrument or is it the system controller sending the data to the instrument?. This chip can be used to implement the GPIB interface of an instrument or any other device.

When you mean assert the line, is it a 5 volts or a 0 volts level?. The GPIB bus uses inverse logic so asserting a line is actually putting o volts on the line.

It would also be interesting to know the state of the other two handshaking lines. Is the interaction between the lines that would determine if there's a problem with the handshaking.

DiegoF.
National instruments.