Siemens SIMATIC TIWAY 1 - Manual (Page 194)

USING THE BDLC PROTOCOL
UNILINK HOST ADAPTER B–9
USER MANUAL
D RNR — The Receive Not Ready command is used by the adapter to
indicate that its input buffer is full and the host should stop
transmitting I-Frames and poll with RRs until the adapter responds
with an RR or an I-Frame.
D REJ — The Reject response is used by the adapter to indicate that a
message frame was received out of order.
D FRMR — The Frame Error response is used by the adapter when:
d an BCS error free I-Frame is received with a control field that is
invalid or not implemented or
d an I-Frame or UI is received with an information field that exceeds
the maximum buffer size or
d
an BCS error free I-Frame is received with an invalid N(R) from
the host computer.