Texas Instruments 990 User Manual page 224

Throughput
The fields shown are as follows:
*
Packet header, consisting of:
*
*
VCG, the FCCC line number to which the device is
attached. This is a default value accepted during
network generation.
LeN, the HDLC drop address. This is also a
default value accepted during network generation.
peR), the receive packet level counter
peS), the transmit (send) packet level counter
Message type, always set to 0007 for a data packet
Destination and Source IDs coded in binary coded decimal
and assigned during network generation
*
User data/message. The maximum size is usually 256 or
260 bytes.
B.7.5 CRC Fields
The CRC fields are two-byte (l6-bit) cyclic redundancy checks
generated at the transmitting station. The receIvIng station
also generates a CRC and compares it with the received value.
This CRC is the CRC-CCITT polynomial.
B-12 2270526-9701