AD73360 datasheet(29/35 Pages) AD

29 / 35 page

REV. A

AD73360

–29–

APPENDIX B

Programming a Single AD73360 for Mixed Mode Operation

This section describes a typical sequence in programming a

single AD73360 to operate in Mixed Mode. The device is con-

figured in Nonframe Sync Loop-Back (see Figure 14), which

allows the DSP’s Tx Register to determine how many words are

sent to the device during one sample interval. In Nonframe

Sync Loop-Back mode care must be taken when writing to the

AD73360 that an ADC result or register read result contained

in the device’s serial register is not corrupted by a write. The

best way to avoid this is to only write control words when the

AD73360 has no more data to send. This can limit the number

of times a DSP can write to the AD73360 and is dependant on

the SCLK speed and the number of channels powered up. In

this example it is assumed that there are only two channels

powered up and that there is adequate time to transmit data

after the ADC results have been read.

In Step 1, the device has just been reset and the on first output

event the AD73360 presents an invalid ADC sample word

Once this word has been received the DSP can begin transmit-

ting programming information to the AD73360. The first con-

trol word sets the sampling rate at 8 kHz. In Step 2, the DSP

instructs the AD73360 to power up channels 1 and 2 and sets

the gain of each. No data is read from the AD73360 at this

point. Steps 3 and 4 set the reference and places the part into

Mixed Mode. In Steps 5 and 6 valid ADC results are read from

the AD73360 and in Step 7 the DSP sends an instruction to the

AD73360 to change the gain of Channel 1.

NOTE

1This sequence assumes that the DSP SPORT’s Rx and Tx interrupts are

enabled. It is important to ensure there is no latency (separation) between

control words in a cascade configuration. This is especially the case when

programming Control Register B, as it contains settings for SCLK and

DMCLK rates.

DSP Tx REG

CONTROL WORD

1000 0001 0000 0011

DEVICE 1

ADC WORD 1*

0000 0000 0000 0000

DSP Rx REG

0000 0000 0000 0000

STEP 1

DON'T CARE

DSP Tx REG

CONTROL WORD

1000 0011 1111 1010

DEVICE 1

ADC WORD 1*

1011 1001 0000 0011

DSP Rx REG

0000 0000 0000 0000

STEP 2

DON'T CARE

DSP Tx REG

CONTROL WORD

1000 0010 1110 0000

DEVICE 1

ADC WORD 1*

1011 1011 1111 1010

DSP Rx REG

0000 0000 0000 0000

STEP 3

DON'T CARE

DSP Tx REG

CONTROL WORD

1000 0000 0000 0010

DEVICE 1

ADC WORD 1*

1011 1010 1110 0000

DSP Rx REG

0000 0000 0000 0000

STEP 4

DON'T CARE

DSP Tx REG

CONTROL WORD

0111 1111 1111 1111

DEVICE 1

ADC WORD 1

1000 0000 0000 0000

DSP Rx REG

1000 0000 0000 0000

STEP 5

ADC WORD 1

DSP Tx REG

CONTROL WORD

0111 1111 1111 1111

DEVICE 1

ADC WORD 2

1111 0000 0000 0000

DSP Rx REG

1111 0000 0000 0000

STEP 6

ADC WORD 2

DSP Tx REG

CONTROL WORD

1000 0011 1000 0010

DEVICE 1

INVALID DATA

xxxx xxxx xxxx xxxx

DSP Rx REG

1111 0000 0000 0000

STEP 7

ADC WORD 2

SET 8kHz SAMPLING

POWER UP CHANNEL 1&2 AND SET GAINS

POWER UP REFERENCE

SET MIXED MODE

CHANGE GAIN ON CHANNEL 1

RECEIVE VALID ADC DATA

*ADC DATA RECEIVED BY THE DSP DURING THE PROGRAMMING PHASE SHOULD NOT BE CONSIDERED VALID RESULTS

Figure 33. Programming a Single AD73360 for Operation in Mixed Mode

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