Motorola DSP56309 User Manual page 168

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 ESSIs in the DSP56309: ESSI0 and ESSI1. For
the sake of simplicity, a single generic ESSI is described.
The ESSI block diagram appears in Figure 7-1 on page 7-5. This interface is synchronous
because all serial transfers are synchronized to a clock.
Note: This should not be confused with the asynchronous mode of the ESSI, in
which separate clocks 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.
Additional synchronization signals are used to delineate the word frames. Normal mode
is used to transfer data at a periodic rate, one word per period. Network mode is similar
in that it is also intended for periodic transfers; however, it supports up to 32 words
(time slots) per period. Network mode can be used to build time division multiplexed
(TDM) networks. In contrast, 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.
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).
7.2 ENHANCEMENTS TO THE ESSI
The synchronous serial interface (SSI) used in the DSP56000 family has been enhanced in
the following ways to make the ESSI:
¥ Network enhancements
Ð Time slot mask registers (receive and transmit) added
Ð End-of-frame interrupt added
Ð Drive enable signal added (to be used with transmitter 0)
MOTOROLA
Enhanced Synchronous Serial Interface (ESSI)
DSP56309UM/D
Introduction
7-3