CS5521 datasheet(38/56 Pages) CIRRUS

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CS5521/22/23/24/28

DS317F8

SCLKs for each Setup referenced are required to

read the conversion words from the data FIFO. The

first 8 SCLKs are used to clear the SDO flag. Ev-

ery 24 bits thereafter consist of the data words of

each Setup that was referenced, until all of the data

has been read from the part. If, during the first 8

SCLKs, "0000 0000" is provided on SDI, the con-

verter will remain in this conversion mode, and be-

gin performing the next set of conversions. To exit

this conversion mode, "1111 1111" must be pro-

vided on SDI during the first 8 SCLKs. If the user

decides to exit, 24 more SCLKs for each referenced

Setup are required to read the final conversion data

set from the FIFO and return to command mode.

1.4.2 Calibration Protocol

To perform a calibration, the user must send a com-

mand byte with its MSB=1, its pointer bits

(CSRP3-CSRP0) set to address the desired Setup to

be calibrated, and the appropriate calibration bits

(CC2-CC0) set to choose the type of calibration to

be performed. Proper calibration assumes that the

CSRs have been previously initialized because the

information concerning the physical channel, its

filter rate, gain range, and polarity, comes from the

channel-setup register being addressed by the

pointer bits in the command byte.

Once the CSRs are initialized, all future calibra-

tions can be performed with one command byte.

Once a calibration cycle is complete, SDO falls and

the results are stored in either the gain or offset reg-

ister for the physical channel being calibrated. Note

that if additional calibrations are performed on the

same physical channel referenced by a different

Setup with different filter rates, gain ranges, or con-

version modes, the last calibration results will re-

place the effects from the previous calibration as

only one offset and gain register is available per

physical channel. One final note is that only one

calibration is performed with each command byte.

To calibrate all the channels additional calibration

commands are necessary.

1.4.3 Example of Using the CSRs to Perform

Conversions and Calibrations

Any time a calibration command is issued (CB=1

and proper CC2-CC0 bits set) or any time a normal

conversion

command

issued

(CB=1,

CC2=CC1=CC0=0, MC=0), the bits D6-D3 (or

CSRP3 - CSRP0) in the command byte are used as

pointers to address one of the Setups in the chan-

nel-setup registers (CSRs). Five example situations

that a user might encounter when acquiring a con-

version or calibrating the converter follow. These

examples assume that the user is using a CS5528

(16 Setups) and that its CSRs are programmed with

the following physical channel order:

6, 1, 6, 2, 6, 3, 6, 4, 6, 5, 6, 2, 6, 7, 6, 8.

Example 1:

The configuration register has the following bits as

shown:

DP3-DP0 = ‘XXXX’,

MC = 0,

L = 0,

RC = X. The command issued is ‘1111 0000’.

These settings instruct the converter to convert the

15th Setup once, as CPB3 - CPB0 = ‘1110’ (which

happens to be physical channel 6 in this example).

SDO falls after physical channel 6 is converted. To

read the conversion results, 32 SCLKs are then re-

quired. Once acquired, the serial port returns to the

command mode.

Example 2:

The configuration register has the following bits as

shown: DP3-DP0 = ‘XXXX’, MC = 0, LP = 1,

RC = 1. The command byte issued is ‘1001 1000’.

These settings instruct the converter to repeatedly

convert the fourth Setup as CPB3-CPB0 = ‘0011’

(which happens to be physical channel 2 in this ex-

ample). SDO falls after physical channel 2 is con-

verted. To read the conversion results 32 SCLKs

are required. The first 8 SCLKs are needed to clear

the SD0 flag. If ‘0000 0000’ is provided to the SDI

pin during the first 8 SCLKs, the conversion is per-

formed again on physical channel 2. The converter

will remain in data mode until ‘1111 1111’ is pro-

vided during the first 8 SCLKs following the fall of

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