Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 781

Powerquicc family

Table of Contents

SCC Transparent Mode

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 configured in the GSMR; see

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 specified in GSMR_L[MODE]. This allows loop-back modes to DMA data

from one memory location to another while data is converted to a specific serial format.

The SCC operations are asynchronous with the core and can be synchronous or asynchronous with other

SCCs. Each SCC 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 non-multiplexed serial interface (NMSI) and

supports modem lines with the general-purpose I/O pins. Data can be transferred either the msb or lsb first

in each octet.

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

Another protocol can be performed on the other half of the SCC

MC68360-compatible SYNC options

SCC Transparent Channel Frame Transmission Process

The transparent transmitter is designed to work almost no intervention from the core. When the core

enables the SCC transmitter in transparent mode, it starts sending idles, which are logic high or encoded

Freescale Semiconductor

Section 21.2.1, "General SCC Mode Register

MPC885 PowerQUICC Family Reference Manual, Rev. 2