Essi Enhancements - Motorola DSP56305 User Manual

7.1 INTRODUCTION
The Enhanced Synchronous Serial Interface (ESSI) provides a full-duplex serial port for
serial communication with a variety of serial devices, including one or more
industry-standard codecs, other DSPs, microprocessors, and peripherals that implement
the Motorola Serial Peripheral Interface (SPI). The ESSI consists of independent
transmitter and receiver sections and a common ESSI clock generator.
There are two independent and identical Enhanced Synchronous Serial Interfaces in the
DSP56305: ESSI0 and ESSI1. For the sake of simplicity, a single generic ESSI is described.
Each ESSI can be accessed through a port, as indicated in Figure 7-2. Any unused ESSI
pins may be used as GPIO pins.
The ESSI has three principal modes of operation, as shown in Figure 7-21. The Normal
mode of operation is used to transfer data at a periodic rate, one word per period. The
Network mode is similar in that it is also intended for periodic transfers; however, it
supports up to 32 words (time slots) per period. The Network mode can be used to build
Time Division Multiplexed (TDM) networks. In contrast, the On-demand mode is
intended for non-periodic transfers of data. This mode can be used to transfer data
serially at high speed when the data become available. This mode offers a subset of the
SPI protocol. The On-demand mode is programmed as a submode of Network mode.
The ESSI block diagram is shown in Figure 7-1. This interface is synchronous because all
serial transfers are synchronized to a clock.
Note: This should not be confused with what is known as the Asynchronous
channels mode of the ESSI, in which separate clocks and frame sync signals
are used for the receiver and transmitter. In this mode, the ESSI is still a
synchronous device, because all transfers are synchronized to these clocks.
Since each ESSI unit can be configured with one receiver and three transmitters, the two
units can be used together for surround sound applications (which need two digital
input channels and six digital output channels). The ESSI can operate with more than
one active transmitter only in Synchronous mode.
7.2

ESSI ENHANCEMENTS

The Synchronous Serial Interface (SSI) used in the DSP56000 family has been enhanced
in the following ways to make the Enhanced Synchronous Serial Interface (ESSI):
MOTOROLA
Enhanced Synchronous Serial Interface (ESSI)
DSP56305 User's Manual
Introduction
7-3