PSB 2115
PSF 2115
Functional Description
Semiconductor Group
64
11.97
The state machine for D-channel access in the intelligent NT describes four states and
four types of conditions for state transition:
The number n of D=1 which has to be counted on IOM-2 by the state machine for state
transition T2 is described in the table below:
Note:
D=idle implies that 8 consecutive ’1’ are detected on the D-channel.
States
Ready
The D-channel is transparent to the layer 1 (D
,20
= D
6
) and no
device occupies the D-channel (BAC=1). The echo bits
correspond to the received D-bits on the S-interface. The layer 2
is blocked (S/G=1) until the required number (priority) of D=1 are
counted on IOM-2.
This state is identical to the ’Ready’ state, except the layer 2 may
also start transmission on the D-channel (S/G=0).
The D-channel is transparent to the layer 1 and occupied by a
source on the S-interface. The layer 2 is blocked (S/G=1).
The D-channel is occupied by the IPAC D-channel controller or
by another D-channel controller on IOM-2. This is indicated by
BAC=0. The Echo-bits are set to ‘D’ (terminals on S are blocked).
State transition conditions
T1
A terminal on the S-interface has started transmission on the D-
channel (D
S
=0). Preceeding this, the required number of D=1
(according to the priority setting) was written and read back
(E-bits) on the S-interface.
T2
The required number of D=1 is counted on the IOM-2 interface,
so the IPAC D-channel controller may start transmission again.
T3
The IPAC layer 2 controller has started transmission on the
D-channel (D
D
= idle).
T4
The IPAC layer 2 controller has stoped transmission on the
D-channel (D
D
= idle), i.e. the end flag of the previous frame or
an abort is detected.
Idle
S Access
Local Access
Previous transmission of NT D-channel controller
successful
(end flag seen)
n = 9
n = 11
not successful
(abort seen)
Configured Priority
Prio = 8 (SCFG:PRI=0)
Prio = 10 (SCFG:PRI=1)
n = 8
n = 10