Table 30-23 Ssi Operating Modes - Motorola DragonBall MC9328MX1 Reference Manual

Synchronous Serial Interface (SSI)
30.5 SSI Operating Modes
The SSI has three basic operating modes, with the option of asynchronous or synchronous protocol for
most modes.
• Normal mode
— asynchronous protocol
— synchronous protocol
• Network mode
— asynchronous protocol
— synchronous protocol
• Gated clock mode
— synchronous protocol only
The mode of the SSI is determined by several bits in the SSI control registers. Table 30-23 lists these
operating modes and gives examples of applications that typically use each mode.
TX, RX Sections
Asynchronous
Asynchronous
Synchronous
Synchronous
Synchronous
The transmit and receive sections of the SSI can be synchronous or asynchronous. In synchronous mode,
the transmitter and the receiver use a common clock and frame synchronization signal. In asynchronous
mode, the transmitter and receiver each have their own clock and frame synchronization signals.
Continuous or Gated clock mode can be selected. In continuous mode, the clock runs continuously. In
gated clock mode, the clock is only functioning during transmission.
Normal or network mode also can be selected. In normal mode, the SSI functions with one data word of
I/O per frame. In network mode, a frame can contain between 2 and 32 data words. Network mode is
typically used in star or ring-time division multiplex networks with other processors or codecs, allowing
interface to time division multiplexed networks without additional logic. Use of the gated clock is not
allowed in network mode. These distinctions result in the basic operating modes that allow the SSI to
communicate with a wide variety of devices.
The SSI supports both normal and network modes, and these can be selected regardless of whether the
transmitter and receiver are synchronous or asynchronous. Typically these protocols are used in a periodic
manner, when data is transferred at regular intervals, such as at the sampling rate of an external codec.
Both modes use the concept of a frame. The beginning of the frame is marked with a frame sync when
programmed with continuous clock. The frame sync occurs at a periodic interval. The length of the frame
is determined by the DC field in either the SRCCR or STCCR register, depending on whether data is being
transferred or received. The number of words transferred per frame depends on the mode of the SSI.
In normal mode, one data word is transferred per frame. In network mode, the frame is divided into
anywhere between 2 and 32 time slots, when one data word can optionally be transferred in each time slot.
30-38
Table 30-23. SSI Operating Modes
Serial Clock Mode
Continuous Normal
Continuous Network
Continuous Normal
Continuous Network
Gated Normal
MC9328MX1 Reference Manual
Typical Application
Multiple synchronous codecs
TDM codec or DSP networks
Multiple synchronous codecs
TDM codec or DSP network
SPI-type devices; DSP to MCU
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