Operational Description
The ISAC-S supplies IOM timing signals as long as there is no DIU command in the C/I (C/I0)
channel. If timing signals are no longer required and activation is not yet requested, this is
indicated by programming DIU in the CIX0 register.
As an alternative to activation via IDP1 (DU), the IOM interface can be activated by setting the
CFS bit to "0". The activation of FSC1 and DCL in this case is similar to figure 73. Note that
the IOM interface can be deactivated through DIU (power-down state, figure 72) only if CFS
is set to logical "1".
In NT mode the IOM interface is activated by the upstream unit turning on the clocking signals.
Simultaneously the upstream unit must send the desired command in the C/I channel. In the
case where activation is requested from a terminal, the layer 1 of ISAC-S in the NT first
requests timing on the IOM interface by pulling IDP0 to a static low level which causes a CISQ
interrupt. Power-up state is entered immediately after timing has been applied. The clock
signals may be switched off after the code Deactivation Indication Downstream has been sent
twice by the upstream unit.
3.3.2
Activation/Deactivation of S/T Interface
Assuming the ISAC-S has been initialized with the required features of the application, it is now
ready to transmit and receive messages in the D channel (LAPD support).
But as a prerequisite, the layer 1 has to be activated.
The layer-1 functions are controlled by commands issued via the CIXR/CIX0 register. These
commands, sent over the IOM C/I channel 0 to layer 1, trigger certain procedures, such as
activation/deactivation, switching of test loops and transmission of special pulse patterns.
These are governed by layer-1 state diagrams in accordance with CCITT I.430. Responses
from layer 1 are obtained by reading the CIRR/CIR0 register after a CISQ interrupt (ISTA).
The state diagrams are shown in figures to . The activation/deactivation implemented by the
ISAC-S in its different operating modes agrees with the requirements set forth in CCITT
recommendations. State identifiers F1-F8 (TE/LT-T) and G1-4 (NT/LT-S) are in accordance
with CCITT I.430. In the NT mode the four states have been expanded to implement a full
handshake between the ends of the subscriber loop.
In the state diagrams a notation is employed which explicitly specifies the inputs and outputs
on the S interface and in the C/I channel: see figure 74.
Semiconductor Group
170
INFINEON [ Infineon ]
