Allen-Bradley 1779-KFMR User Manual page 95

Chapter 6
HDLC Data Link Layer
6 26
This data frame has an address of 1, a send sequence number of 3, and a
receive sequence number of 7. The notation we use here to represent a
supervisory frame is:
This receive ready frame has an address of 3 and a receive sequence
number of 4. The notation we use here to represent an unnumbered frame
is:
This disconnect frame has an address of 1. The examples that follow
show the frames on both circuits with time passing from left to right.
The first example shows a sequence of frames that might occur
immediately after start-up. The SABM command and UA response bring
the link into the data transfer state. The RR command and RR response
let each node know that the other is ready to receive data frames. Data
frame 3,D0,0 is transmitted on circuit BA during the time that both 1,D0,0
and l,D1,0 are transmitted on circuit AB. Therefore, response frame
1,RR2 acknowledges both 1,D0,0 and 1,D1,0. Data frame l,D3,1
acknowledges data frame 3,D0,0.
Circuit AB
1,SABM 1,RR0
Circuit BA
1,UA
3,RR4
1,DISC
1,D0,0 1,D1,0
1,RR0 3,D0,0
1,D2,0 1,D3,1
1,RR2 1,RR3 1,RR4