Texas Instruments 990 User Manual page 222

Throughput
B.7.l Flag Fields
The flag byte is used at the start and end of the transmission
block as a delimiter. Its value is binary 01111110 (>7E). Zero-
bit insertion begins with the first byte after the start flag and
ends at the second cyclic redundancy check (eRe) byte.
B.7.2 Address Field
The address field is the HDLe or drop address. Its value may lie
in the range of 0 through 255; however, in the DX10 HDLC
Communication Package, the upper limit is 63 if the secondary
stations are any combination of TX5s, PM550s, or TM990s.
B.7.3 Command Field
'The command field is the HDLC command/response byte. All valid
values for this byte are given in the following list:
Commands Sent
by Primary
Information (I) Frames:
I
Responses Accepted
by Primary Meaning
I
Information transfer
Numbered Supervisory (S) Frames:
RR
RNR
REJ
SIM
, Unnumbered (U) Frames:
UI
SNRM
DISC
RR
RNR
REJ
RIM
UA
DM
CMDR
B-IO
Receive ready
Receive not ready (busy)
Reject
Set initialization
mode (download)
Request initialization
mode (download)
Unnumbered information
transfer
Unnumbered acknowledge
Set normal
response mode
Disconnect command
I am disconnected
Command (frame) reject
2270526-9701
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