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ADS124S08: Internal temperature sensor

Dimas Ramalho
Prodigy 30 points

Part Number: ADS124S08

Hi Dimas,

Welcome to the E2E forum! What reference are you using in your configuration?  Usually it is best to use the internal reference when using the system monitor.  Have you verified your communication with an oscilloscope or logic analyzer?  If so, can you send me shots of the communication?  Also it would be helpful to know all the device configuration register settings and the schematic.

The most common issues with communication is using the wrong phase of the SCLK and not holding CS low throughout the entire communication transaction.

Best regards,

Bob B

Dimas Ramalho <dimas.ramalho@microsad.com.br>
Anexos11:41 (há 1 hora)
para TI
Hi Bob,
I think that SPI is OK because I can read correctly analog signals from any input, as well digital signals from GPIOs. By the way, I'm using SPI mode 0, because when I started using mode 1 (as described in datasheet) nothing worked. I'm using PIC32MX in this application.
The configuration used is:
SYS: 0x51
INPMUX: 0x6C
PGA: 0x69
DATARATE: 0x02
REF: 0x39 
To read Internal temperature sensor:
RDATA:
Status Read
LSB from MSW
MSB from LSW
LSB from LSW
Best regards,
Dimas Ramalho.TH701V5.pdf
  • 0
    TI__Guru** 113765 points

    Hi Dimas,

    As you have the START pin pulled low, did you issue the START command to start the conversion?  Converting the internal temperature sensor is the same as any other analog input and requires that a conversion take place before attempting to read the result.

    Also, you must verify your communication with a scope or logic analyzer to make sure that there are not any timing issues relative to the opto isolation.  I am also concerned that you are actually transmitting correctly with data changing on the rising edge of SCLK and holding steady on the falling edge of SCLK.  Also, SCLK should be dwelling low.  CS should remain low throughout the entire communication transaction.  As far as the PIC32 the settings should be CPOL = 0 equates to CKP = 0 (idle state for clock is a low level) and CPHA = 1 equates to CKE = 0 (defined as serial output data changes on transition from idle clock state to active clock state) which is what the ADS124S08 datasheet calls Mode 1.

    I also noticed that in your schematic that you do not have the required 330nF (or greater) capacitor between AVDD and AVSS.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    TI__Guru** 113765 points

    Hi Dimas,

    Did you make any further progress?  If not, are you able to send me the shots of the communication?

    Best regards,

    Bob B