XTR108: Unused bits in Control Registers

Part Number: XTR108

According to the datasheet for the XTR108, the registers with unused bits should be filled with '0'.  Using your calibration software and development board it appears that for PGA Gain, PGA input and Iref, the software is filling with '1's.  Can you tell me if there's any issues with filling unused bits with '1' instead of "0'.

Example of the register content after going through calibration using the development software for -50 to 150 PT100:

0 Control 1 = 0x00

1 Reserved = 0x00

2 Reserved = 0x00

3 Fault Status = 0x00

4 Control 2 = 0x01

5 Over/Under-Scale = 0x17

6 PGA Gain = 0xFB

7 Alarm Config. = 0x00

8 PGA Input Config. = 0x8A

9 I_REF Output Config = 0x8A

10 Fine I_REF Adjust = 0x47

11 Coarse I_REF Adjust = 0x0C

12 Fine Zero Adjust = 0x30

13 Coarse Zero Adjust = 0xFE

14 Linearization Adjust = 0xD6

15 Checksum = 0x7D

1 Reply

  • Hi David,
    The automatic calibration process on the XTR108EVM shouldn't set any of the reserved bits during normal operation. That said, the XTR108EVM loads its initial register map from the XTR108, which in turn loads from the attached EEPROM. If the EEPROM contents have reserved bits set, the EVM software will preserve that state. This can be corrected by setting the reserved bits back to 0, then selecting "Write EEPROM" on the Registers tab, followed by "Write All Reg". From here, you can re-calibrate if desired, and the reserved bits should not be set.


    Alex Davis

    Precision Amplifier Applications - TI Tucson