AnsweredAssumed Answered

AD7766 daisy chain SPI problem

Question asked by franzwi on Oct 27, 2015
Latest reply on Oct 30, 2015 by MClifford

Hello, i have trouble with the AD7766  in daisy chain mode. Ich have 3 ADC's in daisy chain. The MCLK is generated by a RC oscillator with a frequency of 91kHz. At the power up of the SOC i generate a syn pulse for all 3 ADC's. I use a standard SPI on a Cypress CY8C5. Spi Mode is 0,0. The SPI CLK is 4Mhz. With the DRDY signal i generate a interrupt and in the service routine i read 72 bit from the ADC.

My problem happens every 8th  til 16th DRDY signal the ADC's delivers wrong values. But it happens only on some analog input voltages. That is what confuses me. If i change the SPI CLK frequecy it happens every 8th for example.

The ADC's work with about 5,6kHz. here you can see a log of the data from the ADC'S.

If i generate a Sync pule every 8th ADC conversion the problem is gone. But i loose a many time after a SYNC pulse.

 

thank you

Franz

 

613392  4895355 4895915

614191  4895403 4895915

612734  4898800 4895915

613491  4895447 4895915

4896158 7770835 7772009

614387  4900299 4900012

614428  4899518 4900012

615655  4898117 4895915

613866  4899479 4900012

612482  4896561 4895915

613343  4894488 4891818

614342  4897015 4895915

614129  4897721 4895915

613453  4899683 4900012

615186  4897176 4895915

615152  4892754 4891818

611615  4900270 4900012

612798  4895143 4895915

612542  4898357 4895915

612233  4894026 4891818

4895481 7771001 7772009

613297  4899211 4900012

612994  4898587 4895915

614319  4892535 4891818

615058  4899170 4900012

615151  4898398 4895915

613691  4899022 4900012

612665  4896313 4895915

614097  4888832 4887721

612455  4897753 4895915

612813  4899421 4900012

614332  4897230 4895915

614105  4897288 4895915

613336  4900140 4900012

614224  4897749 4895915

613309  4898486 4895915

4889642 7772754 7772009

612856  4895368 4895915

611031  4899558 4900012

610774  4897419 4895915

611722  4897419 4895915

613999  4898597 489591

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