ADS8668 unpredictable behaviour

Hi Jay,

Thanks for choosing our SAR ADC. I’m trying to understand what you are doing and what you want to do from your MOSI commands without more information:

MOSI                               MISO    

0000001 0 00000000      0000000000000000 (R)    -- Are you trying to read “AUTO_SEQ_EN” register? How many SCLKs you sent for this operation?

0000001 1 00011110      0000111100000000 (W)   -- Are you trying to write “AUTO_SEQ_EN” register with “00011110”? How many SCLKs?

0000001 1 00011100      0000111000000000 (W)   -- Are you trying to write “AUTO_SEQ_EN” register with “00011100”? How many SCLKs?

0000001 1 00011000      0000110000000000 (W)   -- Are you trying to write “AUTO_SEQ_EN” register with “00011000”? How many SCLKs?

0000001 1 00010000      0000100000000000 (W)   -- Are you trying to write “AUTO_SEQ_EN” register with “00010000”? How many SCLKs?

0000001 1 00000000      0000000000000000 (W)   -- Are you trying to write “AUTO_SEQ_EN” register with “00000000”? How many SCLKs?

0000000 1 00000000      0000111111111111      -- Nothing you did with the data on MOSI

0000001 1 00011110      0000111100000000 (W)   -- Are you trying to write “AUTO_SEQ_EN” register with “00011110”? How many SCLKs?

1100 0000 0000 0000   0000111100000000 (MAN_CH_0)   -- How many SCLKs you sent for this operation after /CS falling edge?

……

Generally, it will be very helpful to understand if the timing screenshot for SPI signals can be uploaded(SCLK,SDI,SDO and /CS). Thanks.

Regards

Dale Li

Hi Dale,

Thanks for your reply. The problem which i posted in the earlier post has been resolved, i guess that the above observation is because of MOSI commands were sent out at wrong clock edge.

But now i'm stuck with a different issue. When i write try to configure,

MSB to LSB
EX :1
AUTO_SEQ_EN 0000001 1 00101101 - trying to activate channel 5,3,2,0 with 16 clock pulse.

Output was "00100000"

EX :2
AUTO_SEQ_EN 0000001 1 00111101 - trying to activate channel 5,4,3,2,0 with 16 clock pulse.

Output was "00111100"

According to the data sheet, it should write back exactly what was written on to the program registers. So my inference is that SDO of ADC can't able to switch back to HIGH once it falls from HIGH to LOW.

And after writing a configuration value, when i read the program register, its all set back to default value.

EX :3

AUTO_SEQ_EN 0000001 1 00101101 - trying to activate channel 5,3,2,0 with 16 clock pulse.

Output was "00100000"

AUTO_SEQ_EN 0000001 0 00000000 - trying to read back

Output was "11111111"


When i try to read the ADC value from the a input channel manually - where 3V dc input was given.

EX :4

MAN_CH_0 11000000 00000000 - trying to read the ADC value from channel 0

Output was "111111111111" - 12 bit high

the same ouput was thrown for every channel i read manually and also through AUTO_RST

Clock pulse settings:

354 ns - clock high time
354 ns - clock low time

SCLK freq : 1.4 MHz approx

First clock 235 ns after CS pulled down.

next 16 clock pulses for MOSI - data send out at raising clock edge

next 16 clock pulse for MISO - data collected at falling clock edge
 
After completing 32 clock pulse, it waits for 118 ns and then CS pulled back to High

I try to capture the screen shot from the Oscilloscope, it seems bit tricky with my new Oscilloscope. Once i get the pics, I will upload it. Please let me know is there anything wrong with my operation ?

regards,
Jay