Datasheet

AD7734 Data Sheet
Rev. A | Page 20 of 32
MODE REGISTER
8 Bits, Read/Write Register, Address 38h–3Bh, Default Value 00h
The mode register configures the part and determines its operating mode. Writing to the mode register clears the ADC status register, sets
the
RDY
pin to a logic high level, exits all current operations, and starts the mode specified by the mode bits.
The AD7734 contains only one mode register. The two LSBs of the address are used for writing to the mode register to specify the channel
selected for the operation determined by the MD2 to MD0 bits. Only the address 38h must be used for reading from the mode register.
Bit Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Mnemonic MD2 MD1 MD0 CLKDIS DUMP Cont RD 24/16 BIT CLAMP
Default 0 0 0 0 0 0 0 0
Bit Mnemonic Description
7–5 MD2–MD0 Mode Bits. These three bits determine the AD7734 operation mode. Writing a new value to the mode bits will
exit the part from the mode in which it has been operating and place it in the newly requested mode
immediately. The function of the mode bits is described in more detail below.
4 CLKDIS Master Clock Output Disable. When this bit is set to 1, the master clock is disabled from appearing at the
MCLKOUT pin and the MCLKOUT pin is in a high impedance state. This allows turning off the MCLKOUT as a
power saving feature. When using an external clock on MCLKIN, the AD7734 continues to have internal clocks
and will convert normally regardless of the CLKDIS bit state. When using a crystal oscillator or ceramic resonator
across the MCLKIN and MCLKOUT pins, the AD7734 clock is stopped and no conversions can take place when the
CLKDIS bit is active. The AD7734 digital interface can still be accessed using the SCLK pin.
3 DUMP DUMP Mode. When this bit is reset to 0, the channel status register and channel data register will be addressed
and read separately. When the DUMP bit is set to 1, the channel status register will be followed immediately by a
read of the channel data register regardless of whether the status or data register has been addressed through
the communication register. The continuous read mode will always be dump mode reading of the channel status
and data register, regardless of the dump bit value (see the Digital Interface Description section for more details).
2 Cont RD When this bit is set to 1, the AD7734 will operate in the continuous read mode (see the Digital Interface
Description section for more details).
1 24/16 BIT The Channel Data Register Data Width Selection Bit. When set to 1, the channel data registers will be 24 bits
wide. When set to 0, the channel data registers will be 16 bits wide.
0 CLAMP This bit determines the channel data register’s value when the analog input voltage is outside the nominal input
voltage range. When the CLAMP bit is set to 1, the channel data register will be digitally clamped either to all 0s
or all 1s when the analog input voltage goes outside the nominal input voltage range. When the CLAMP bit is
reset to 0, the data registers reflect the analog input voltage even outside the nominal voltage range (see the
Analog Input’s Extended Voltage Range section).
MD2 MD1 MD0 Mode Address Used for Mode Register Write Specifies:
0 0 0 Idle Mode
0 0 1 Continuous Conversion Mode The First Channel to Start Converting
0 1 0 Single Conversion Mode Channel to Convert
0 1 1 Power-Down (Standby) Mode
1 0 0 ADC Zero-Scale Self-Calibration Channel Conversion Time Used for the ADC Self-Calibration
1 0 1 For Future Use
1 1 0 Channel Zero-Scale System Calibration Channel to Calibrate
1 1 1 Channel Full-Scale System Calibration Channel to Calibrate