User`s guide

42 DC 900-1317J
ADCCP NRM Programmer’s Guide
F-bit checkpoint recovery occurs when the primary station receives a supervisory frame
or I-frame with the F-bit set and finds that the N(R) field in the received frame does not
acknowledge the N(S) field in the last I-frame the primary station sent with the P-bit
set. Figure 2–4 shows that F-bit checkpoint recovery is shared by all three modes (NRM,
ARM, and ABM).
P-bit checkpoint recovery occurs when the secondary station receives a supervisory
frame or I-frame with the P-bit set and finds that the N(R) field in the received frame
does not acknowledge the N(S) field in the last I-frame the secondary station sent with
the F-bit set. Figure 2–4 shows that P-bit checkpoint recovery is shared by the NRM and
ARM modes only. The ABM mode does not use P-bit recovery.