Original question:
ADS8867: ADS8867 GPIO/SPI mode can not get correct adc value
Hi,
I have observed that first reading from ADS8867 by the 3-wire SPI interface, seems to be garbage.
Is this normally behavior or have I maybe missed something? See code read ex. below from the prototype.
Regards,
Peter
| read no. | code |
| 1 | -19185 |
| 2 | 23184 |
| 3 | 23205 |
| 4 | 23159 |
| 5 | 23199 |
| 6 | 23134 |
| 7 | 23166 |
| 8 | 23178 |
| 9 | 23144 |
| 10 | 23170 |
| 11 | 23150 |
Hello Peter,
Thank you for your post.
I believe it does make sense to discard the first ADC sample. Notice in Figure 1 that the normal 3-wire SPI frame begins with the conversion period, followed the acquisition of the next sample voltage. During this first conversion period, the sampled voltage is from the "previous acquisition," meaning whatever voltage was present on the internal sampling capacitors during startup is the value being converted. Once you convert this value, the next acquisition period will sample the proper input signal.
Regards,
Ryan
