
USING THE BDLC PROTOCOL
UNILINK HOST
ADAPTERB–5
USER MANUAL
B.2.5
Block Checksum Field
This
two-byte field is the Block Checksum (BCS) calculated by the transmitter
and checked by the receiver to detect transmission errors. The calculation is a
16-bit
one’
s complement Fletcher Checksum.
The BCS is calculated using all bytes in the transmitted frame except the
starting and ending flags (DLE-STX and DLE-ETX), the BCS bytes, and any
inserted
DLEs. The method for calculating and checking the BCS is discussed in
Paragraph
B.7.
Figure B–3 illustrates how a TIWAY I Primitive is enclosed in the adapter
command
string which is enclosed in the BDLC I-Frame.
Length Primitive
Code Descriptor
Field(s) Data Unit
Field(s)
Command Code Secondary
Address Network Data
TIWAY I Primitives
DLE–STX Control FSC
UNILINK Host Adapter Commands
Adapter
Address DLE–ETX
BDLC Protocol I–Frame
Adapter
Data
Figure B–3 Illustrative BDLC I-Frame