SYNCHRONOUS SERIAL INTERFACE (SSI)
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PORT C
MOTOROLA
6.4
SYNCHRONOUS SERIAL INTERFACE (SSI)
The synchronous serial interface (SSI) provides a full-duplex serial port for serial commu-
nication with a variety of serial devices including one or more industry-standard codecs,
other DSPs, microprocessors, and peripherals which implement the Motorola SPI.
The user can independently define the following characteristics of the SSI: the number of
bits per word, the protocol, the clock, and the transmit/receive synchronization.
The user can select among three modes: normal, on-demand, and network. The normal
mode is typically used to interface with devices on a regular or periodic basis. The da-
ta-driven on-demand mode is intended to be used to communicate with devices on a non-
periodic basis. The network mode provides time slots in addition to a bit clock and frame
synchronization pulse.
The SSI functions with a range of 2 to 32 words of I/O per frame in the network mode. This
mode is typically used in star or ring time division multiplex networks with other DSP56K
processors and/or codecs. The clock can be programmed to be continuous or gated.
Since the transmitter and receiver sections of the SSI are independent, they can be pro-
grammed to be synchronous (using a common clock) or asynchronous with respect to
each other.
The SSI requires up to six pins, depending on its operating mode. The most common mini-
mum configuration is three pins: transmit data (STD), receive data (SRD) and clock (SCK).
The SSI consists of independent transmitter and receiver sections and a common SSI
clock generator. Three to six pins are required for operation, depending on the operating
mode selected.
The following is a short list of SSI features:
• Three-Pin Interface:
TXD – Transmit Data
RXD – Receive Data
SCLK – Serial Clock
• A 10 Mbps at 40 MHz (f
osc
/4) serial interface
• Double Buffered
• User Programmable
• Separate Transmit and Receive Sections
• Control and Status Bits
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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