PCM1850

PCM1851

SLES108 − MARCH 2004

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22

HPF Bypass Control

The built-in HPF function for dc component rejection can be bypassed via the serial port. In bypass mode, the dc component

of the analog input signal, the internal dc offset, etc., are converted and included in the digital output data.

BYP

HPF (HIGH-PASS FILTER) MODE

0

Normal (no dc component on DOUT) mode (default)

1

Bypass (dc component on DOUT) mode

System Reset Control

The system reset control is used to resynchronize the system via the serial port when the system clock frequency, interface

mode, and data format are changed. Change them while SRST = LOW. If they are changed during normal operation, analog

performance can be degraded.

SRST

SYSTEM RESET

0

Resynchronization

1

Normal operation (default)

Mode Register Reset Control

The MRST bit is used to reset the mode control register to its default settings via the serial port.

MRST

MODE REGISTER RESET

0

Set default value

1

Normal operation (default)

SPI SERIAL CONTROL PORT FOR MODE CONTROL (PCM1850)

The user-programmable built-in functions of the PCM1850 can be controlled through a serial control port with the SPI

format. All operations for the serial control port use 16-bit data words. Figure 27 shows the control data word format. The

most significant bit must be set to 0. There are seven bits, labeled IDX[6:0], that set the register index (or address) for write

operations. The least significant eight bits, D[7:0], contain the data to be written to the register specified by IDX[6:0].

Figure 28 shows the functional timing diagram for writing to the serial control port. MS (pin 30) is held at a logic 1 state until

a register needs to be written. To start the register write cycle, MS is set to logic 0. Sixteen clocks are then provided on MC

(pin 31), corresponding to the 16 bits of the control data word on MD (pin 32). After the sixteenth clock cycle has completed,

the data is latched into the indexed mode control register in the write operation. To write the next data word, MS must be

set to 1 once.

MSB

LSB

Register Index (or Address)

Register Data

0

IDX6

IDX5

IDX4

IDX3

IDX2

IDX1

IDX0

D7

D6

D4

D5

D3

D2

D1

D0

Figure 27. Control Data Word Format for MD

IDX0

D7

D6

D4

D5

D3

D2

D1

D0

MS

MC

MD

IDX1

IDX2

IDX3

IDX4

IDX5

IDX6

0

X

X

X

0

IDX6

Figure 28. Serial Control Format