DSP56857 datasheet(310/662 Pages) FREESCALE

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Functional Description

5685X Digital Signal Controller User Manual, Rev. 4

12-10

Freescale Semiconductor

12.5 Functional Description

The ESSI has two basic operating modes. Table 12-5 lists these operating modes and some of the

typical applications. These distinctions result in the basic operating modes allowing the ESSI to

communicate with a wide variety of devices. These modes can be programmed by several bits in

the ESSI control registers. For additional information, please see Section 12.8.

The ESSI supports both Normal and Network modes, and these can be selected independently of

whether the transmitter and receiver are synchronous or asynchronous. Typically these protocols

are used in a periodic manner, where data is transferred at regular intervals, such as at the

sampling rate of an external codec. Both modes use the concept of a frame. The beginning of the

frame is marked with a frame sync.

The frame sync occurs at a periodic interval. The length of the frame is determined by the DC and

WL field bits in either the SRXCR or STXCR register, depending on whether data is being

transmitted or received. The number of words transferred per frame depends on the mode of the

ESSI.

12.5.1 Normal Mode

Normal mode is the simplest mode of the ESSI. It is used to transfer one word per frame. A frame

sync occurs at the beginning of each frame. The length of the frame is determined by the

following factors:

•

The period of the serial bit clock (PSR, PM bits for internal clock or the frequency of the

external clock on the SCK or SC0 pin)

•

The number of bits per sample (WL) bits

•

The number of time slots per frame (DC) bits

Table 12-5.

ESSI Operating Modes

TX, RX Sections1

In the Synchronous mode, the transmitter and receiver use a common clock and frame sychronization signal.

In the Asynchronous mode the transmitter and receiver operate independently on their own clocks and frame

syncs.

Serial Clock

Mode2

In the Normal mode, the ESSI only transmits during the first time-slot of each I/O frame. In the Network mode,

any number from 2 to 32 data words of I/O per frame can be used. The Network mode is typically used in star

or ring time division multiplex networks with other processors or codecs, allowing interface to TDM networks

without additional logic.

Typical Application

Asynchronous

Continuous

Normal

Multiple Asynchronous Codecs

Asynchronous

Continuous

Network

TDM Codec or DSC Networks

Synchronous

Continuous

Normal

Multiple Synchronous Codecs

Synchronous

Continuous

Network

TDM Codec or DSC Network

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