Texas Instruments 990 User Manual page 243

Communications Structures
The following format depicts a complete data packet after the
header has been added:
BIT NUMBER
o
2 3
4 5 6
......
-
...
• 0 - __ . • • •
BYTE 0
Q 0 0 0 VCG
LOGICAL CHANNEL. NUMBER (L.CN)
2 P (R)
I
0
P (S)
3
0 0
0
0 0 0 0
4 0 0 0 0
0 1 1
5 DID DID
6
DID DID
7
SID SID
8 SID SID
9
USER
MESSAGE
n
2280625
where:
7
I
0
0
1
T
x.
25 DATA PACKET
HEADER
+
MESSAGE TYPE
t
DESTINATION
AND
SOURCE IDS
+
USER DATAl
MESSAGE
Bytes 0, 1, 2 are the packet header, consisting of:
2270526-9701
*
A data qualifier bit, Q.
always set to zero.
This is
*
VCG, the line number to which the
device is attached.
*
LeN, the HDLC drop address for the
device.
*
P (R) , the
counter
0-9
receive
packet level