Dear all,
Component : ADS1217 Datasheet : SBAS260C It's explain on the ADS1217's datasheet (p17) : that when the decimation register DEC0 & DEC1are set by default (1920) with a 2.4576MHz crystal, the data rate frequency is 10Hz so the /DRDY output should be at the same frequency.
I check that with the following equation(p24) : Decimation Ratio = Fosc/(mfactor*Fdata) = 2.4576*10^6/(128*10Hz) = 1920
There is my registers setups: SETUP(00h) = 00001110 MUX(01h) = 00001000 ACR(02h) = 01111000 IDAC1(03h) = 11010000 IDAC2(04h) = 00010100 ODAC(05h) = 00000000 DIO(06h) = 00000000 DIR(07h) = 01000000 DEC0(08h) = 10000000 M/DEC1(09h)= 01110111 The others register are set by a SELFCAL command. Problem:
The /DRDY output frequency is 9.4Hz instead of 10Hz...
Questions:
Does this shift is explain on any datasheet? If yes which one?
Does this error is the same with all the components? Thanks you by advance for all yours support. Julien
Have you checked that the fOSC frequency is really 2.4576MHz? Could it be that your crystal is being "pulled" to a lower frequency by inappropriate load caps? With 2.4576MHz exactly going in, you should get 10Hz out on /DRDY with the register settings you have.
In fact the /DRDY clock was ok but when I select an other channel I miss two falling edge.
That why i thought that there was a bad frequency on /DRDY.
But i still don't understand why selecting channel change the DRDY clock?...
Well, it took some digging, but there is an explanation: on the ADS1217, unlike its cousins the ADS1216 and ADS1218, the DRDY is suppressed until the filter fully settles. So since you're using the sinc3 filter setting, whenever you change channels the part holds off sending DRDY until the third conversion after the channel change completes. That's why you're missing two DRDYs when you change channels.
Allright! Thank you for your help.