Is there some sort of buffer for status bytes in some instruments?

Question

I am trying to obtain the state of an HP8160A Pulse Gen. The status Byte consists of the following:
bit 7 not used
bit 6 SRQ bit
bit 5 Unallowed error bit
bit 4 not used
bit 3downto0 error code
I am not interested in the SRQ bit, just the bits related to the error info. Everything works perfectly for some sequences of data entry. Other times it seems that the status byte's information is lagging behind the actual state of the instrument (which is known from the error display on the front panel of the actual instrument).
My understanding of the status byte is that it is stored in a piece of memory that contains info which is updated as soon as that info changes. When a request for
that info is made, the state the instrument is in should be delivered. Is this not correct? Maybe there is some kind of buffer? Also, my limited experience suggests status bytes are a single byte (8 bits), but the VISA ReadSTB function returns 16 bits. Is this a difference between IEEE 488.1 and 488.2 or could this discrepancy be my potential problem?
If you would like to help but need more details, please ask and I will post them ASAP. I am dried up as far as new ideas goes.
Thank you for any insight,
Chris
PS. I have included the complete llb I am using if anyone is interested. An example of the problem I am having can be exhibited with the follwing sequence:
PERIOD
111
ns
us
This should set the period to 111 ns., giving an error, then clicking the us button next should be an acceptable value and the timing error should no longer be reported.
Attachments:
hp8160a.zip ‏508 KB

Answer 1

There are two things I can think of off the top of my head: First, your assumptions about how the instrument should work are correct, it's possible though that the microcontroller in the instrument can't keep up with you. I had an instrument once that would occasionally fail because my computer was so fast it would send the command and check for a status change before the instrumnt had time to read the command from it's internal buffer--and that was with LV V1 running on a MacII! Second, it could be that the error has to be explicitly cleared before you go on. I have seen instruments that latch errors. Hope this helps... Mike....
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