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General Description
In the example shown in Figure 1-4, one SCC channel connects through the NMSI mode to
a commercial packet data network. This connection might be used for remote status moni-
toring or for maintenance functions for a system. Another SCC is used to connect to a local
asynchronous terminal. The other SCC channel is used as a local synchronous channel,
which could connect to another computer or subsystem. The SCP channel could then be
used for local interconnection of interface chips or peripherals to the MC68302-based sys-
tem.
1.5 BASIC RATE ISDN OR DIGITAL VOICE/DATA TERMINAL
A basic rate ISDN (2B + D) or digital voice/data terminal can be made from a chip set based
on the MC68302. Refer to Figure 1-5 for an example of a basic rate ISDN voice/data termi-
nal. In this terminal, the CP can directly support the 2B + D channels and perform either
V.110 or V.120 rate adaption. The physical layer serial interface is connected to the local
interconnection bus (IDL in Figure 1-5, but the GCI and PCM buses can also be supported).
The system then supports one of the B channels for voice (connected directly to the physical
bus). The D channel consists of one SCC port; the other B channel is used for data transfer
through a second SCC port. The data can be routed to a terminal (RS-232 type) via the third
SCC port in the NMSI mode. The SCP functions as a control channel for the IDL bus in this
case.
Some ISDN physical layer devices support the signaling and framing functions of the D
channel. In these cases, the D channel can connect through the microprocessor interface
to the physical layer device, and the extra SCC port can then be used for a second B channel
to transfer data.
The benefit of a local interconnection bus (see Figure 1-5) versus a microprocessor bus is
a lower pin count. It is also easy to maintain this low pin-count interface between several
different interface chips, such as the MC145554 PCM codec/filter monocircuit and the
MC145474 S/T transceiver.
The MC68302 combines the M68000 architecture with a number of peripherals for integrat-
ed applications in communications control. The M68000 core manages the CP through the
on-chip, dual-port RAM and internal registers. The base address of the dual-port RAM and
internal registers is selected through the base address register. Other peripherals are also
accessed and controlled through internal registers: the IDMA controller, the three timers,
I/O ports, and the interrupt controller.
1-6
MC68302 USER'S MANUAL
MOTOROLA
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