Motorola PowerQUICC II MPC8280 Series Reference Manual page 713

Chapter 20
Serial Communications Controllers
(SCCs)
The MPC8280 has four serial communications controllers (SCCs), which can be
configured 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 protocol's link layer (layer 2 of the OSI
reference model). Many SCC functions are common to protocols of the following
controllers:
• UART, described in Chapter 21, "SCC UART Mode."
• HDLC and HDLC bus, described in Chapter 22, "SCC HDLC Mode."
• AppleTalk/LocalTalk, described in Chapter 26, "SCC AppleTalk Mode."
• BISYNC, described in Chapter 23, "SCC BISYNC Mode."
• Transparent, described in Chapter 24, "SCC Transparent Mode."
• Ethernet, described in Chapter 25, "SCC Ethernet Mode."
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).
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 16.3, "NMSI Configuration," for each SCC's available
clock sources. These clocks can be as fast as a 1:4 ratio of the system clock. (For example,
an SCC internal clock can run at 12.5 MHz in a 50-MHz system.) However, an SCC's
ability to support a sustained bit stream depends on the protocol as well as other factors.
MOTOROLA Chapter 20. Serial Communications Controllers (SCCs)
Freescale Semiconductor, Inc.
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