PEB2085 SIEMENS [Siemens Semiconductor Group], PEB2085 Datasheet - Page 55

• Manufacturer Part Number: PEB2085
• Description: ISDN SubscribernAccess Controller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

2.3.8
The C/I channel conveys the commands and indications between the layer-1 and layer-2 parts
of the ISAC-S. This channel is available in all timing modes. Beside being accessed by the
internal layer-2 part, it can also be accessed by an external layer-2 device, e.g. to control the
layer-1 activation/deactivation procedures. This access is arbitrated via the TIC bus access
protocol which is performed in the MONITOR channel.
The C/I channel is accessed via register CIRR (in receive direction, layer-1 to layer-2) and
register CIXR (in transmit direction, layer-2 to layer-1). The C/I code is four bits long.
A listing and explanation of the layer-1 C/I codes can be found in chapter 3.4.
In the receive direction, the code from layer-1 is continuously monitored, with an interrupt being
generated anytime a change occurs (ISTA:CISQ). A new code must be found in two
consecutive IOM frames to be considered valid and to trigger a C/I code change interrupt
status (double last look criterion).
In the transmit direction, the code written in CIXR is continuously transmitted in the C/I
channel.
2.3.9
The arbitration mechanism implemented in the monitor channel of the IOM allows the access
of external communication controllers (up to 7) to the layer-1 functions provided in the ISAC-S
and to the D channel. (TIC bus; see figure 24). To this effect the outputs of the controllers
(ICC:ISDN Communication Controller PEB 2070) are wired-or-and connected to pin IDP1, a
pull-up resistor being already provided in the ISAC-S. The inputs of the ICC’s are connected
to pin IDP0.
Semiconductor Group
Command/Indicate (C/I) Channel Handling
TIC Bus Access
55
Functional Description