Motorola MPC8260 User Manual
MOTOROLA
Chapter 19. Serial Communications Controllers (SCCs)
19-1
Chapter 19
Serial Communications Controllers
(SCCs)
Serial Communications Controllers
(SCCs)
190
190
The MPC8260 has four serial communications controllers (SCCs), which can be
conÞgured independently to implement different protocols for bridging functions, routers,
and gateways, and to interface with a wide variety of standard WANs, LANs, and
proprietary networks. An SCC has many physical interface options such as interfacing to
TDM buses, ISDN buses, and standard modem interfaces.
conÞgured independently to implement different protocols for bridging functions, routers,
and gateways, and to interface with a wide variety of standard WANs, LANs, and
proprietary networks. An SCC has many physical interface options such as interfacing to
TDM buses, ISDN buses, and standard modem interfaces.
The SCCs are independent from the physical interface, but SCC logic formats and
manipulates data from the physical interface. Furthermore, the choice of protocol is
independent from the choice of interface. An SCC is described in terms of the protocol it
runs. When an SCC is programmed to a certain protocol or mode, it implements
functionality that corresponds to parts of the protocolÕs link layer (layer 2 of the OSI
reference model). Many SCC functions are common to protocols of the following
controllers:
manipulates data from the physical interface. Furthermore, the choice of protocol is
independent from the choice of interface. An SCC is described in terms of the protocol it
runs. When an SCC is programmed to a certain protocol or mode, it implements
functionality that corresponds to parts of the protocolÕs link layer (layer 2 of the OSI
reference model). Many SCC functions are common to protocols of the following
controllers:
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HDLC and HDLC bus, described in Chapter 21, ÒSCC HDLC Mode.Ó
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AppleTalk/LocalTalk, described in Chapter 25, ÒSCC AppleTalk Mode.Ó
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Although the selected protocol usually applies both to the SCC transmitter and receiver, one
half of an SCC can run transparent operations while the other runs a standard protocol
(except Ethernet).
half of an SCC can run transparent operations while the other runs a standard protocol
(except Ethernet).
Each Rx and Tx internal clock can be programmed with either an external or internal
source. Internal clocks originate from one of eight baud rate generators (BRGs) or an
external clock pin; see Section 15.3, ÒNMSI ConÞguration,Ó for each SCCÕs available clock
sources. These clocks can be as fast as a 1:2 ratio of the system clock. (For example, an SCC
internal clock can run at 12.5 MHz in a 25-MHz system.) However, an SCCÕs ability to
support a sustained bit stream depends on the protocol as well as other factors.
source. Internal clocks originate from one of eight baud rate generators (BRGs) or an
external clock pin; see Section 15.3, ÒNMSI ConÞguration,Ó for each SCCÕs available clock
sources. These clocks can be as fast as a 1:2 ratio of the system clock. (For example, an SCC
internal clock can run at 12.5 MHz in a 25-MHz system.) However, an SCCÕs ability to
support a sustained bit stream depends on the protocol as well as other factors.