Freescale Semiconductor MPC8260 - Manual (Page 679)

MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor 20-1
Chapter 20
Serial Communications Controllers (SCCs)
The PowerQUICC II 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.
Associated with each SCC is a digital phase-locked loop (DPLL) for external clock recovery, which
supports NRZ, NRZI, FM0, FM1, Manchester, and Differential Manchester. If the clock recovery function
is not required (that is, synchronous communication), then the DPLL can be disabled, in which case only
NRZ and NRZI are supported.
An SCC can be connected to its own set of pins on the PowerQUICC II. This configuration is called the
non-multiplexed serial interface (NMSI) and is described in
Chapter 15, “Serial Interface with Time-Slot
Assigner.” Using NMSI, an SCC can support standard modem interface signals, RTS, CTS, and CD. If
required, software and additional parallel I/O lines can be used to support additional handshake signals.
Figure 20-1 shows the SCC block diagram.