Motorola MPC8260 - Manual (Page 653)

MOTOROLA Chapter 23. SCC Transparent Mode 23-1
Chapter 23
SCC Transparent Mode
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Transparent mode (also called totally transparent or promiscuous mode) provides a clear
channel on which the SCC can send or receive serial data without bit-level manipulation.
Software implements protocols run over transparent mode. An SCC in transparent mode
functions as a high-speed serial-to-parallel and parallel-to-serial converter.
Transparent mode can be used for serially moving data that requires no superimposed
protocol, for applications that require serial-to-parallel and parallel-to-serial conversion for
communication among chips on the same board, and for applications that require data to be
switched without interfering with the protocol encoding itself, such as when data from a
high-speed time-multiplexed serial stream is multiplexed into low-speed data streams. The
concept is to switch the data path without altering the protocol encoded on that data path.
Transparent mode is conÞgured in the GSMR; see Section 19.1.1, ÒThe General SCC Mode
Registers (GSMR1ÐGSMR4).Ó Transparent mode is selected in GSMR_H[TTX, TRX] for
the transmitter and receiver, respectively. Setting both bits enables full-duplex transparent
operation. If only one is set, the other half of the SCC uses the protocol speciÞed in
GSMR_L[MODE]. This allows loop-back modes to DMA data from one memory location
to another while data is converted to a speciÞc serial format.
The SCC operations are asynchronous with the core and can be synchronous or
asynchronous with other SCCs. Each clock can be supplied from the internal baud rate
generator bank, DPLL output, or external pins.
The SCC can work with the time-slot assigner (TSA) or nonmultiplexed serial interface
(NMSI) and supports modem lines with the general-purpose I/O pins. Data can be
transferred either the msb or lsb Þrst in each octet.
23.1 Features
The following list summarizes the main features of the SCC in transparent mode:
¥ Flexible buffers
¥ Automatic SYNC detection on receive
¥ CRCs can be sent and received
¥ Reverse data mode