Élan™SC520 Microcontroller User’s Manual 22-1
CHAPTER
22
SYNCHRONOUS SERIAL INTERFACE
22.1 OVERVIEW
The ÉlanSC520 microcontroller includes a synchronous serial interface (SSI). The SSI
provides efficient full-duplex and half-duplex, bidirectional communication to peripheral
devices. The interface can be used to configure and monitor the status of devices such as
ISDN transceivers, EEPROMs, SLACs, audio CODECs, LCD drivers, DSPs, etc. It can
easily communicate with slave interfaces that are compatible to Motorola’s Serial Peripheral
Interface (SPI), Motorola’s Serial Communication Port (SCP), National Semiconductor
Corporation’s Microwire, and other industry standards.
Features of the SSI include:
■ Full or half-duplex operation
■ Compatible with either four-pin or three-pin peripheral devices
■ Multiple device enables through programmable I/O (PIO) pins
■ Configurable clock idle state and phase
■ Configurable bit shifting order, most significant bit or least significant bit first
■ Programmable SSI clock speed, from 64 kHz to 8 MHz
■ Transaction complete status, available as interrupt
22.2 BLOCK DIAGRAM
A block diagram of the SSI is shown in Figure 22-1. System diagrams, as well as timing
diagrams, of a three-pin SSI interface and a four-pin SSI interface are shown on page 22-3.
22.3 SYSTEM DESIGN
Three SSI pins are provided: clock out (SSI_CLK), data out (SSI_DO), and data in (SSI_DI).
The SSI_DO signal is normally at high-impedance when no transmit transaction is active
on the SSI. An external pullup or pulldown resistor can be added to this pin, if required by
the slave device.
Most slave devices require an enable pin to be asserted during an operation and deasserted
when not in operation. PIO pins on the ÉlanSC520 microcontroller can be used for this
purpose.
Many slave SSI ports provide an interrupt output pin to the ÉlanSC520 microcontroller.
These can be routed to one of the GPIRQx pins, which are multiplexed with PIOs. See
Chapter 15, “Programmable Interrupt Controller”, and Chapter 2, “Pin Information”, for
information on external interrupts.
See the
Élan™SC520 Microcontroller Data Sheet
, order #22003, for timing tables and
additional timing diagrams.
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