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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 Sections
1
1. 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.
2. 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.
Serial Clock
Mode
2
Typical Application
Asynchronous
Asynchronous
Synchronous
Synchronous
Continuous
Continuous
Continuous
Continuous
Normal
Network
Normal
Network
Multiple Asynchronous Codecs
TDM Codec or DSC Networks
Multiple Synchronous Codecs
TDM Codec or DSC Network