Murata Electronics North America XDM2140 Benutzerhandbuch

Example 2: Decoding an HDLC packet received from the XDM2140

To understand how to decode an HDLC packet sent from the XDM2140, let us assume that
the XDM2140 received a Get command with a parameter of XDM2140 information (see
Section 9.3.7), and replied with the following HDLC Packet. (All values are in hexadecimal.)

Start Byte

HDLC Packet Payload (stuffed)

FCS (stuffed)

Stop Byte

8A 07 00 20 00 00 5B 00 01 01 06 00 3C 00 00 00 00 00 00 7D 5E C3
02 00 08 30 30 30 5F 45 56 30 31 00 13 00 00

3E 30

Table 62

Step 1

(HDLC layer) strip off delimiters:

HDLC Packet Payload (stuffed)

FCS (stuffed)

8A 07 00 20 00 00 5B 00 01 01 06 00 3C 00 00 00 00 00 00 7D 5E C3
02 00 08 30 30 30 5F 45 56 30 31 00 13 00 00

3E 30

Table 63

Step 2

Remove byte stuffing:

To remove byte stuffing, check for instances of “7D 5D” or “7D 5E” and replace as follows:

7D 5D

=> 7D

7D 5E

=> 7E

HDLC Packet Payload

FCS

8A 07 00 20 00 00 5B 00 01 01 06 00 3C 00 00 00 00 00 00 7E C3 02 00
08 30 30 30 5F 45 56 30 31 00 13 00 00

3E 30

Table 64

Step 3

Confirm FCS:

Calculate the checksum for the HDLC payload.

HDLC Packet Payload

8A 07 00 20 00 00 5B 00 01 01 06 00 3C 00 00 00 00 00 00 7E C3 02 00
08 30 30 30 5F 45 56 30 31 00 13 00 00

Table 65

Confirm that the FCS matches the FCS sent with the packet. Because the packet encodes
FCS least significant byte first, in this example the calculated FCS should match “30 3E”.

Step 4 (Application layer) parse HDLC payload content:

The resulting packet payload is as follows:

HDLC Packet Payload

8A 07 00 20 00 00 5B 00 01 01 06 00 3C 00 00 00 00 00 00 7E C3 02 00
08 30 30 30 5F 45 56 30 31 00 13 00 00

Table 66