Could you have gotten the two length bytes swapped and are asking for
way too many bytes?
Dar Scott
On Oct 7, 2010, at 6:22 PM, Len Morgan wrote:
I'm trying to read data from a MODBus/TCP controller and having
some issues with the timing of the read command. I request a block
of registers from the slave and it returns the requested bytes and
header just fine and very quickly. In order to read everything
right, I have to first read the first 6 bytes of the header to know
how many bytes are to follow. Once I know that, I do a read from
socket tSock for <bytes> characters. Note that ALL of the
characters have been received in a single packet so once I read the
6 bytes, the rest of the data is already in the socket buffer.
The problem I have is when I do the second read, the read command
blocks for the socketTimeoutInterval before continuing. It doesn't
matter what I set it to, it will wait that long before continuing.
I tried catching the socketTimeout message but that message is
never sent, even when I set the socketTimeoutInterval to 5
milliseconds!
I am not using the read ... with message form of the command since
I want the handler to wait until all the bytes have been received
before I move on. Has anyone else seen this? Have I missed
something in the documentation or could this be something in the
Windows code that handles sockets?
Any help would be appreciated!
len morgan
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