DSP56303 datasheet(135/292 Pages) FREESCALE

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ESSI Data and Control Signals

DSP56303 User’s Manual, Rev. 2

Freescale Semiconductor

7-3

transmitted, the STD signal does not assume a high-impedance state. The STD signal can be

programmed as a GPIO signal (P5) when the ESSI STD function is not in use.

7.2.2 Serial Receive Data Signal (SRD)

SRD

receives serial data and transfers the data to the receive shift register. SRD can be

programmed as a GPIO signal (P4) when the SRD function is not in use.

7.2.3 Serial Clock (SCK)

SCK

is a bidirectional signal providing the serial bit rate clock for the ESSI interface. The signal is

a clock input or output used by all the enabled transmitters and receivers in Synchronous modes

or by all the enabled transmitters in Asynchronous modes. See Table 7-1 for details. SCK can be

programmed as a GPIO signal (P3) when not used as the ESSI clock.

Note:

Although an external serial clock can be independent of and asynchronous to the DSP

system clock, the external ESSI clock frequency must not exceed Fcore/3, and each

ESSI phase must exceed the minimum of 1.5 CLKOUT cycles. The internally sourced

ESSI clock frequency must not exceed Fcore/4.

7.2.4 Serial Control Signal (SC0)

ESSI0: SC00; ESSI1: SC10

To determine the function of the SC0 signal, select either Synchronous or Asynchronous mode,

according to Table 7-2. In Asynchronous mode, this signal is used for the receive clock I/O. In

Synchronous mode, this signal is the transmitter data out signal for transmit shift register TX1 or

for serial flag I/O. A typical application of serial flag I/O would be multiple device selection for

addressing in codec systems.

If SC0 is configured as a serial flag signal or receive clock signal, its direction is determined by

the Serial Control Direction 0 (SCD0) bit in ESSI Control Register B (CRB). When configured as

an output, SC0 functions as the serial Output Flag 0 (OF0) or as a receive shift register clock

Table 7-1. ESSI Clock Sources

SYN

SCKD

SCD0

RX Clock Source

RX Clock

Out

TX Clock Source

TX Clock Out

Asynchronous

EXT, SC0

—

EXT, SCK

—

INT

SC0

EXT, SCK

—

EXT, SC0

—

INT

SCK

INT

SC0

INT

SCK

Synchronous

0/1

EXT, SCK

—

EXT, SCK

—

0/1

INT

SCK

INT

SCK

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