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ADS1261: REFL_ALM bit getting set

Prodigy 30 points

Replies: 3

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Part Number: ADS1261


I am using the sample code provided for ADS1261. I am able to write the configuration registers and also read back it with correct data.

But when i try to read the status byte (add: 01h), I am getting  REFL_ALM bit getting set which means reference voltage is below the low limit. I have enable internal reference voltage by setting REFENB bit in REF Register.

Can you help me with possible reasons for REFL_ALM getting set.

Thanks in advance.

  • Hi Mahesh,

    In addition to setting the REFENB bit in the REF register, you also need to select the correct reference configuration using the RMUXP and RMUXN bits (in the same REF register). Have you selected the internal reference using these bits? The default is AVDD and AVSS.

    If you can share your schematic and register settings that would help.


  • In reply to Bryan Lizon86:


    I am using the reference code share for ADS1261 with changes in few registers

        initRegisterMap[REG_ADDR_ID]             =     0x00;           /* NOTE: This a read-only register */
        initRegisterMap[REG_ADDR_STATUS]         =     STATUS_CLEAR;    /* NOTE: This a non-default setting */
        initRegisterMap[REG_ADDR_MODE0]            =     0x4C;            
        initRegisterMap[REG_ADDR_MODE1]         =     0x41;    
        initRegisterMap[REG_ADDR_MODE2]         =     0x30;
        initRegisterMap[REG_ADDR_MODE3]         =     0x00;    
        initRegisterMap[REG_ADDR_REF]             =     0x15;    
        initRegisterMap[REG_ADDR_OFCAL0]         =     OFCAL0_DEFAULT;
        initRegisterMap[REG_ADDR_OFCAL1]         =     OFCAL1_DEFAULT;
        initRegisterMap[REG_ADDR_OFCAL2]         =     OFCAL2_DEFAULT;
        initRegisterMap[REG_ADDR_FSCAL0]         =     FSCAL0_DEFAULT;
        initRegisterMap[REG_ADDR_FSCAL1]         =     FSCAL1_DEFAULT;
        initRegisterMap[REG_ADDR_FSCAL2]         =     FSCAL2_DEFAULT;
        initRegisterMap[REG_ADDR_IMUX]             =     0x4A;    
        initRegisterMap[REG_ADDR_IMAG]             =     0x66;    
        initRegisterMap[REG_ADDR_RESERVED]         =     RESERVED_DEFAULT;
        initRegisterMap[REG_ADDR_PGA]             =     PGA_DEFAULT;
        initRegisterMap[REG_ADDR_INPMUX]        =     0x98;    
        initRegisterMap[REG_ADDR_INPBIAS]        =     INPBIAS_DEFAULT;

    Please review and let me know if there is any mistake.

  • In reply to Mahesh Adsul1:

    Hi Mahesh,

    Some comments:

    • In MODE0 register, you are selecting 1200 SPS data rate and the FIR filter (0100 1100), which is not a valid combination. The FIR filter is only valid on data rates up to 20 SPS.
    • In MODE1 register, you are turning on the 2-wire AC excitation mode (0100 0001), which uses the AIN2 and AIN3 pins. This will cause issues for your GPIO pins (which we discussed in a separate e2e post)
    • In REF register, you are turning the internal reference on but selecting AVDD and AVSS as the reference source. I would suggest selecting the internal VREF as the reference source and seeing if this changes anything (RMUXP = 00, RMUXN = 00). For your RTD measurements, make sure to select AIN0 and AIN1 as the reference input (RMUXP = RMUXN = 10)