CS5541 datasheet(17/26 Pages) CIRRUS

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CS5541

DS500PP1

2.9.6 System Calibration

If a system level calibration is to be performed us-

ing a system microcontroller, it is best to put the

converter in the Continuous Conversions with De-

fault Calibration Coefficients mode. The user

would configure the system with a zero-level input

and store the resulting conversion for system offset

correction. Then the user would configure the sys-

tem with a full-scale input level and store the re-

sulting conversion for system full-scale correction.

Correction of converter data is then performed us-

ing the system microcontroller.

2.9.7 Reading Conversions

At the completion of a conversion, SDO will fall to

logic 0 to indicate that the conversion is complete.

If calibration modes are used they will be transpar-

ent to user and only affect the effective throughput

of the ADC. Nevertheless, to read a conversion

word, the user must issue 8 SCLKs (SDI = logic 0

for the NULL command and remain in this mode or

SDI can be used to clock in a new command) to

clear the SDO flag and read the status flags. Upon

the falling edge of the 8th SCLK, the SDO pin will

present the first bit (MSB) of the conversion word.

24 SCLKs (high, then low) are then required to

read the conversion word from the port. Upon the

falling edge of the 32nd SCLK, SDO will return

high, waiting till the next conversion is complete

before it falls again.

When operating in any of the conversion modes,

the user need not read every conversion. If the user

chooses not to read a conversion after SDO falls,

SDO will rise one MCLK clock cycle before the

next conversion is completed and then fall to signal

that another conversion word is available. To exit

the particular conversion mode, the user must issue

any valid command, other than the NULL com-

mand, to the SDI input. The new command can be

issued anytime other than during the data read. If

the user wants to read the last conversion data and

issue the new command, the following protocol is

required: After SDO falls, read the status flags

(keeping SDI low, 8 SCLKs), followed by the con-

version data (24 SCLKs). Then follow it up with

the new command at SDI (8 SCLKs).

If the command happens to be a power save com-

mand, the serial port goes back to the command

mode. Otherwise, the conversion will stop in

progress and start new conversions based on the in-

formation in the command byte, and the serial port

remains in the data mode.

Note:

1) If the user begins to clear the SDO end-of-

conversion flag and read the conversion data,

this action must be finished before the

conversion cycle which is occurring in the

background is complete if the user wants to

be able to read the new conversion data.

2) If a new conversion command is issued to

the converter while it is performing a

conversion, the filter will stop the current

conversion and start a new convolution cycle

to perform a new conversion.

3) If a new conversion command is issued

when SDO is low, SDO will output 01111,

then CH, OD, and OF. Afterwards, SDO will

remain high until one MCLK cycle before the

new data is ready, then fall to indicate that the

conversion is completed.

2.9.8 Output Coding

The CS5541 outputs 24-bit data conversion words.

To read a conversion word the user must read the

conversion data register. The conversion data reg-

ister is 24 bits long and outputs the data word MSB

first. Once a conversion is complete, SDO falls and

32 SCLK’s are required to read the results. The first

8 SCLKs are used to clear the SDO flag and clock

out the status flags.

The Channel Indicator (CH) bit keeps track of

which input channel was converted.

The Oscillation Detect (OD) bit is set to a logic 1 any

time that an oscillatory condition is detected in the

modulator. This does not occur under normal oper-

ating conditions, but may occur whenever the input

to the converter is extremely overranged. If the OD

bit is set, the conversion data bits can be completely

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