CS5531-AS datasheet(17/52 Pages) CIRRUS

17 / 52 page

CS5531/32/33/34

DS289PP5

Using the single conversion mode, an 8-bit com-

mand word can be written into the serial port. The

command includes pointer bits which ‘point’ to a

16-bit command in one of the Channel Setup Reg-

isters which is to be executed. The 16-bit Setups

can be programmed to perform a conversion on any

of the input channels of the converter. More than

one of the 16-bit Setups can be used for the same

analog input channel. This allows the user to con-

vert on the same signal with either a different con-

version speed, a different gain range, or any of the

other options available in the channel setup regis-

ters. Alternately, the user can set up the registers to

perform different conversion conditions on each of

the input channels.

The ADCs also include continuous conversion ca-

pability. The ADCs can be instructed to continu-

ously convert, referencing one 16-bit command

Setup. In the continuous conversions mode, the

conversion data words are loaded into a shift regis-

ter. The converter issues a flag on the SDO pin

when a conversion cycle is completed so the user

can read the register, if need be. See the section on

Performing Conversions for more details.

The following pages document how to initialize the

converter, perform offset and gain calibrations, and

how to configure the converter for the various con-

version modes. Each of the bits of the configuration

scribed. A list of examples follows the description

section. Also the Command Register Quick Refer-

ence can be used to decode all valid commands (the

first 8-bits into the serial port).

2.2.1. System Initialization

The CS5531/32/33/34 provide no power-on-reset

function. To initialize the ADCs, the user must per-

form a software reset by resetting the ADC’s serial

port with the Serial Port Initialization sequence.

This sequence resets the serial port to the command

mode and is accomplished by transmitting at least

15 SYNC1 command bytes (0xFF hexadecimal),

followed by one SYNC0 command (0xFE hexa-

decimal). Note that this sequence can be initiated at

anytime to reinitialize the serial port. To complete

the system initialization sequence, the user must

also perform a system reset sequence which is as

follows: Write a logic 1 into the RS bit of the con-

figuration register. This will reset the calibration

registers and other logic (but not the serial port). A

valid reset will set the RV bit in the configuration

logic 1, wait 20 microseconds, then write the RS bit

back to logic 0. While this involves writing an en-

tire word into the configuration register, the RV bit

is a read only bit, therefore a write to the configu-

ration register will not overwrite the RV bit. After

clearing the RS bit back to logic 0, read the config-

uration register to check the state of the RV bit as

this indicates that a valid reset occurred. Reading

the configuration register clears the RV bit back to

logic 0.

Completing the reset cycle initializes the on-chip

registers to the following states:

Note:

Previous datasheets stated that the RS bit

would clear itself back to logic 0 and therefore

the user was not required to write the RS bit

back to logic 0. The current data sheet

instruction that requires the user to write into

the configuration register to clear the RS bit

has been added to insure that the RS bit is

cleared. Characterization across multiple lots

of silicon has indicated some chips do not

automatically reset the RS bit to logic 0 in the

configuration register, although the reset

function is completed. This occurs only on

small number of chips when the VA- supply is

negative with respect to DGND. This has not

caused an operational issue for customers

because their start-up sequence includes

writingaword(with RS=0) intothe

configuration register after performing a

reset. The change in the reset sequence to

Configuration Register:

00000000(H)

Offset Registers:

00000000(H)

Gain Registers:

01000000(H)

Channel Setup Registers: 00000000(H)

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