Datasheet AD7711A (Analog Devices) - 9

AD7711A Control Register (24 Bits)
A write to the device with the A0 input low writes data to the control register. A read to the device with the A0 input low accesses the contents of the control register. The control register is 24 bits wide and when writing to the register 24 bits of data must be written; otherwise the data will not be loaded to the control register. In other words, it is not possible to write just the first 12 bits of data into the control register. If more than 24 clock pulses are provided before TFS returns high, then all clock pulses after the 24th clock pulse are ignored. Similarly, a read operation from the control register should access 24 bits of data.
MSB 2 MD2 MD1 MD0 G2 G1 G0 CH PD WL IO BO B/U FS11* FS10 FS9 FS8 FS7 FS6 FS5 FS4 FS3 FS2 FS1 FS0
*Must always be 0 to ensure correct operation of the device.
FS0 Operating Mode MD2 MD1 MD0 Operating Mode
0 0 0 Normal Mode. This is the normal mode of operation of the device whereby a read to the device with A0 high accesses data from the data register. This is the default condition of these bits after the internal power-on reset. 0 0 1 Activate Self-Calibration. This activates self-calibration on the channel selected by CH. This is a one-step calibration sequence, and when complete, the part returns to normal mode (with MD2, MD1, MD0 of the control register returning to 0, 0, 0). The DRDY output indicates when this self-calibration is complete and valid data is available in the output register. For this calibration type, the zero-scale calibration is done internally on shorted (zeroed) inputs, and the full-scale calibration is done internally on VREF. 0 1 0 Activate System Calibration. This activates system calibration on the channel selected by CH. This is a two-step calibration sequence, with the zero-scale calibration done first on the selected input channel and DRDY indicating when this zero-scale calibration is complete. The part returns to normal mode at the end of this first step in the two-step sequence. 0 1 1 Activate System Calibration. This is the second step of the system calibration sequence with full-scale calibration being performed on the selected input channel. Once again, DRDY indicates when the full- scale calibration is complete. When this calibration is complete, the part returns to normal mode. 1 0 0 Activate System Offset Calibration. This activates system offset calibration on the channel selected by CH. This is a one-step calibration sequence and, when complete, the part returns to normal mode with DRDY indicating when this system offset calibration is complete. For this calibration type, the zero-scale calibration is done on the selected input channel, and the full-scale calibration is done internally on VREF. 1 0 1 Activate Background Calibration. This activates background calibration on the channel selected by CH. If the background calibration mode is on, then the AD7711A provides continuous self-calibration of the reference and shorted (zeroed) inputs. This calibration takes place as part of the conversion sequence, extending the conversion time and reducing the word rate by a factor of 6. Its major advantage is that the user does not have to worry about recalibrating the device when there is a change in the ambient temperature. In this mode, the shorted (zeroed) inputs and VREF, as well as the analog input voltage, are continuously monitored, and the calibration registers of the device are automatically updated. 1 1 0 Read/Write Zero-Scale Calibration Coefficients. A read to the device with A0 high accesses the contents of the zero-scale calibration coefficients of the channel selected by CH. A write to the device with A0 high writes data to the zero-scale calibration coefficients of the channel selected by CH. The word length for reading and writing these coefficients is 24 bits, regardless of the status of the WL bit of the control register. Therefore, when writing to the calibration register 24 bits of data must be written; otherwise the new data will not be transferred to the calibration register. 1 1 1 Read/Write Full-Scale Calibration Coefficients. A read to the device with A0 high accesses the contents of the full-scale calibration coefficients of the channel selected by CH. A write to the device with A0 high writes data to the full-scale calibration coefficients of the channel selected by CH. The word length for reading and writing these coefficients is 24 bits, regardless of the status of the WL bit of the control register. Therefore, when writing to the calibration register, 24 bits of data must be written; otherwise the new data will not be transferred to the calibration register. REV. D –9–