Theory Of Operation - Sharp LH79524 User Manual

Chapter 14
Synchronous Serial Port
The Synchronous Serial Port is a master or slave interface that enables synchronous serial
communication with slave or master peripherals in one of three modes:
• Motorola SPI
• Texas Instruments DSP-compatible synchronous serial interface
• National Semiconductor Microwire.
The SSP incorporates two 16-bit-wide, 8-entry-deep FIFOs, one for transmitting data and
one for receiving data.The transmit FIFO takes data written to it and transmits it on the
serial interface. The receive FIFO parallellizes the serial data stream and presents it in a
FIFO for access by other devices. If the receive FIFO is not empty, the SSP can assert an
interrupt after a specified number of clock ticks elapses following the start of a receive
transfer. This feature permits interrupt-driven data transfers that are greater than the FIFO
watermark, but not an even multiple of it.
The SSP also features:
• Programmable clock rate
• Programmable data frame size, from 4 to 16 bits. Each frame transmits most-significant
bit first.
• Single combined interrupt is an OR function of the individual interrupt requests.
• Loopback Test Mode.

14.1 Theory of Operation

The SSP is a master or slave interface for synchronous serial communication with slave
peripheral devices that have Motorola SPI, National Semiconductor Microwire, or Texas
Instruments DSP-compatible synchronous serial interfaces. The SSP performs serial-to-
parallel conversion on data received from a peripheral device. The transmit and receive
paths are buffered with internal FIFO memories. These memories can store eight 16-bit
values independently in both transmit and receive modes. Serial data is transmitted on the
SSPTX pin and received on the SSPRX pin.
During transmission, data writes to the transmit FIFO via the APB interface. The transmit
data is queued up for parallel-to-serial conversion onto the transmit interface. The transmit
logic formats the data into one of three basic frame types:
• Motorola SPI
• Texas Instruments DSP-compatible Synchronous Serial Interface
• National Semiconductor Microwire.
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