Hi,

>>
Talking to the identical app. (under development) on another PC using a NULL modem cable.

No Handshaking (per the spec of the app. I will ultimately be talking to).
At other end (testing) I display count of received and data received. Sending 12 bytes but getting only 8. At that point I have no idea how to get the other 4 to be sent.

I'll check the CTS and DSR but assume they're OK.

RThreshold set to 1, SThreshold set to 0 (tried 1 too, no joy).
No error checking coded yet. I must add some at this point.
>>

To clarify: is the data sticking in the Send Buffer or just getting lost in transmission ? (If there's no handshaking it should all get transmitted) If it just doesn't arrive that may indicate a buffer overrun - are you checking for comEventOverrun in the OnComm of the receiving end ?

Are you working in event driven (i.e using OnComm()) or polling mode ?

Few thoughts:
If you're not using any handshaking then RTS/CTS values aren't going to be relevant.
Is the data straight ASCII or binary - if binary then the InputMode property may have an effect ?
If you're using OnComm() and the message is of known length you could try setting the RThreshold accordingly on the receiving end.
Can you test using HyperTerminal to emulate the other app ?

HTH,
VIv