CS5460 datasheet(18/34 Pages) CIRRUS

18 / 34 page

CS5460

DS279PP5

3.2 Serial Port Interface

The CS5460’s serial interface consists of four con-

trol lines: CS, SDI, SDO, and SCLK.

CS, Chip Select, is the control line which enables

access to the serial port. If the CS pin is tied to logic

0, the port can function as a three wire interface.

SDI, Serial Data In, is the data signal used to trans-

fer data to the converters.

SDO, Serial Data Out, is the data signal used to

transfer output data from the converters. The SDO

output will be held at high impedance any time CS

is at logic 1. Figure 10 illustrates the serial se-

quence necessary to write to, or read from the serial

port’s buffers.

SCLK, Serial Clock, is the serial bit-clock which

controls the shifting of data to or from the ADC’s

serial port. The CS pin must be held at logic 0 be-

fore SCLK transitions can be recognized by the

port logic. To accommodate opto-isolators SCLK

is designed with a Schmitt-trigger input to allow an

opto-isolator with slower rise and fall times to di-

rectly drive the pin. Additionally, SDO is capable

of sinking or sourcing up to 5 mA to directly drive

an opto-isolator LED. SDO will have less than a

400 mV loss in the drive voltage when sinking or

sourcing 5 mA.

As shown in Figure 10 a transfer of data is always

initiated by sending the appropriate 8-bit command

(MSB first) to the serial port (SDI pin). It is impor-

tant to note that some commands use information

from the cycle-counter and configuration registers

to perform the function. For those commands it is

important that the correct information is written to

those registers first.

When a command involves a write operation the

serial port will continue to clock in the data bits

(MSB first) on the SDI pin for the next 24 SCLK

cycles. When a read command is initiated the serial

port will start transferring register content bit serial

(MSB first) on the SDO pin for the next 8, 16, or 24

SCLK cycles depending on the command issued.

The micro-controller is allowed to send a new com-

mand while reading register data. The new com-

mand will be acted upon immediately and could

possibly terminate the register read. During the

read cycle, the SYNC0 command (NOP) should be

strobed on the SDI port while clocking the data

from the SDO port.

3.3 Serial Port Initialization

The serial port is initialized to the command mode

whenever a reset is performed or when the port ini-

tialization sequence is completed. The port initial-

ization sequence involves clocking 3 (or more)

SYNC1 command bytes (0xFF) followed by

SYNC0 command byte (0xFE). This sequence

places the chip in the command mode where it

waits until a valid command is received.

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