confused about serial read buffer

[JJoe]

I am communicating with a motor controller via the serial port, and through search I've solved most of my problems.  However, I'm getting some behavior I don't understand with the buffer and serial read.

For every command I send, there is a response.  What I'd like to do is essentially this:

SEND command

SEND command

READ response

where the first command is just an initialization to which I'm not terribly interested in the response, and the second is a query.  If I do it as above, I end up reading a different response every time as it seems to cycle through the buffer of input strings.

SEND command

FLUSH buffer

SEND command

READ response

exhibits the same behavior, but with some empty strings mixed in.

SEND command

READ response

SEND command

READ response

also cycles through various inputs, while:

FLUSH buffer

SEND command

READ response

SEND command

READ response

seems to work ok.  I must be misunderstanding what VISA flush buffer actually flushes, because I feel like {SEND FLUSH SEND READ} should work for me.  I'm sure there are far more grevious inefficiencies in my code than extra serial read commands, but I'd rather not depend on matching them up so precisely in order to be reading the correct status.

[Dennis_Knutson]

If you are immediately doing a flush buffer after the write and you see unexpected responses then next time you do a read, I suspect that the instrument is still sending (or hasn't sent anything yet) after the flush is executed. I suppose you could put a wait after the first write and then do a flush buffer but I think the best solution is to do a read after every write like you have in the last example.

[JJoe]

ahh, good point-- most likely that flush is getting rid of non or half-written commands.  Thanks!