GetStartStopMsg not returning data

[Mikla]

I am using the following to return data from a device (Davis Weather Station), but I am not getting any data.

Code:

BytesRead := GetStartStopMsg(m_Port, WaitFor, 06, 21, MaxBytes, ToFill);

The format of the data coming back is 100 bytes:

ACK + 99 byte data packet (LF CR CRC are the last four bytes of the packet)

I use 21(NAK) for the terminator since I know it should not be in the data packet and count on MaxBytes (set to 100) to get all the data. I then will do a CRC check on the data to validate it.

In debugging, I get zero for BytesRead. Yet if I do

Code:

BytesRead := GetTermedMsg(m_Port, WaitFor, 10, 13, True, ToFill);

I will get 96 bytes back in BytesRead, but I lose the CRC value. How can I get all 100 bytes?

Thanks.

[jrlewis]

The way the docs read the GetStartStopMsg should work as you expect it to. To get the last 2 bytes use either the ReadBuffer or ReadByte method of the ComPort class. I wish folks that came up with these protocols would frame messages with either start/stop or just a stop byte to make it easy to capture them. The buggers are the ones where you have to figure out what type of message it is first before you know how many bytes you need to expect.

[Dean Roddey]

You'd just do the 10/13 and upon return issue a read for 2 more bytes. Kind of a wierd protocol.

[Mikla]

OK, I did the two reads and that seems to work... though, it appears my checksum calc is a bit messed up.

Yeah, the protocol is a bit odd. I am a bit worried about the number of fields. I am over 40 already and I havn't even done the High/Low data or the alarms.