Serial Port Woes

[Len Morgan]

I'm having a lot of trouble consistently reading a serial port.  I'm 
trying to talk to a microcontroller using ModBus ASCII and the basic 
idea is to send a request for data (about 12 bytes) and then wait for an 
answer (about 300 bytes).  There is between a 1/4 and 1/2 second delay 
from when I send the command and the controller STARTS sending it back.

I also can't get it to work at all if I open it for update (either text 
or binary).  I have to open the com port, send the command, then close 
the port and reopen it for read to get anything at all.

I've tried "until linefeed", "until empty", "until eof", "for 1 line", 
etc. and none of them seem to work reliably.  I KNOW that a response 
ends with a CRLF pair and there is only ever 1 "line" in a response so 
if I could just wait until I got the LF and it happened in say 3 seconds 
or less, I'd be happy.

Any suggestions??

len morgan