SYNCHRONOUS SERIAL INTERFACE (SSI)
6 - 112
PORT C
MOTOROLA
6.4.7
Operating 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 net-
work 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 arbitra-
tion. An SPI master device always uses an internally generated clock; whereas, an SPI
slave device always uses an external clock.
6.4.7.1
Data/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.
6.4.7.1.1
Normal/Network Mode Selection
Selecting between the normal mode and network mode is accomplished by clearing or set-
ting 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
Operating
Format
Serial
Clock
TX, RX
Sections
Typical Applications
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
Table 6-17 SSI Operating Modes
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Freescale Semiconductor, Inc.
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