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vrf OBJECT PROPERTIES

Question asked by jcmartin on Jun 3, 2003

Hello Hugo,
If the protocol has, as you say, the number of bytes in the header
(viz A packet size indicator),
then assuming the header is always a fixed number of bytes,
you first do a binary read of the standard number of bytes
for the header then parse that and compute how many more
bytes to read, then do a binary read for that number of bytes
and Voila'....

We have a bit more complex protocol to deal with here, DF1.
Which has no packet size indicator, the packet starts with
an escape sequence and ends with an escape sequence,
so we have to read it one byte at a time and have to analyze
each byte as it comes in (a real royal pain - but the PC's
are pretty fast today so it is not very noticeable).

Regards
....Rob





"Hugo Renkema" <TKIP@gastec.nl> on 06/05/2003 06:33:38 AM

Please respond to "Hugo Renkema" <TKIP@gastec.nl>

To:    "VEE vrf" <vrf@it.lists.it.agilent.com>
cc:

Subject:    [vrf] No read terminator symbol RS232 communication




Hello everyone,



This is my first post in the vrf Mailing List. I hope my problem is
explained well, if not; feel free to ask for more information.



I am using HP-VEE 6.01 to communicate with a device via RS232. The protocol
by which the communication takes place has no EOL-symbol. The message-body
does contain a NoB (Number of Bytes) which indicates the length of the
message.



When sending commands from PC to this device, this is not a problem in
HP-VEE. The problem occurs when the device sends back a response. This
response also has no EOL-symbol. Therefore HP-VEE doesn't know when the
total message is received.



This results in the fact that the response is shown in the BUS I/O MONITOR,
but not available with a read-command in a DIRECT IO component.



This is due to the fact that the read terminator, which must be filled in,
is different for every single response.



The question is simple (and hopefully the answer too). How to read a
string, obtained from a COM-port, using HP-VEE when the last byte of the
message is unknown.



Thanks in advance,





Hugo Renkema

Email: tkip@gastec.nl


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