There is an HDLC_test.c sample that comes with the Dynamic C 9, you can use this sample as a reference to implement
HDLC application for Rabbit 6000. In Dynamic C 10, we have provided the library file HDLC_PACKET.LIB related to HDLC, you can find at the below directory
Please go through section 20.3.2 HDLC Mode (Page number: 205) from the Rabbit 5000 processor reference manual at the below link.
Here mentioned that what are the steps you need to do in the HDLC mode.
Also please go through the following thread at the Digi forum, .