Compaq LA36 Service Manual page 113

(2) RS-423 serial interface
Read data
DSR
ST D D D D D D D D SP
0 1 2 3 4 5 6 7
RD
Transmitted data
TR
ST D
D D D D D D D SP
0 1 2 3 4 5 6 7
SD
Figure 5.24 RS-423 serial interface signal timing