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Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

SYNCHRONOUS SERIAL INTERFACE (SSI)

Table 6-17 SSI Operating Modes

Operating

Serial

TX, RX

Typical Applications

Format

Clock

Sections

 

 

 

 

 

 

 

 

 

Normal

Continuous

Asynchronous

Single Asynchronous Codec; Stream-Mode Channel Interface

 

 

 

 

Normal

Continuous

Synchronous

Multiple Synchronous Codecs

 

 

 

 

Normal

Gated

Asynchronous

DSP-to-DSP; Serial Peripherals (A/D,D/A)

 

 

 

 

Normal

Gated

Synchronous

SPI-Type Devices; DSP to MCU

 

 

 

 

Network

Continuous

Asynchronous

TDM Networks

 

 

 

 

Network

Continuous

Synchronous

TDM Codec Networks, TDM DSP Networks

 

 

 

 

On Demand

Gated

Asynchronous

Parallel-to-Serial and Serial-to-Parallel Conversion

 

 

 

 

On Demand

Gated

Synchronous

DSP to SPI Peripherals

 

 

 

 

6.4.7Operating Modes – Normal, Network, and On-Demand

The SSI has three basic operating modes and many data/operation formats. These modes can be programmed by several bits in the SSI control registers. Table 6-17 lists the SSI operating modes and some of the typical applications in which they may be used.

The data/operation formats are selected by choosing between gated and continuous clocks, synchronization of transmitter and receiver, selection of word or bit frame sync, and whether the LSB is transferred first or last. The following paragraphs describe how to select a particular data/operation format and describe examples of normal-mode and net- work-mode applications. The on-demand mode is selected as a special case of the network mode.

The SSI can function as an SPI master or SPI slave, using additional logic for arbitration, which is required because the SSI interface does not perform SPI master/slave arbitration. An SPI master device always uses an internally generated clock; whereas, an SPI slave device always uses an external clock.

6.4.7.1Data/Operation Formats

The data/operation formats available to the SSI are selected by setting or clearing control bits in the CRB. These control bits are MOD, GCK, SYN, FSL1, FSL0, and SHFD.

6.4.7.1.1Normal/Network Mode Selection

Selecting between the normal mode and network mode is accomplished by clearing or setting the MOD bit in the CRB (see Figure 6-55). For normal mode, the SSI functions with one data word of I/O per frame (see Figure 6-56). For the network mode, 2 to 32 data words of

6 - 112 PORT C MOTOROLA

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