if you want to make sure, you may decide to use the wait modifier.

On the send side, you use something like...
Code:
HSEROUT ["UUUU-OK",ByteA, ByteB, ByteC, ByteD]
on the receiver side...
Code:
HSERIN [WAIT("OK"),ByteA, ByteB, ByteC, ByteD]
For your first test, just remove the transceiver, if it's working, add them.