Location Mnemonic Description
MR12 B/U Bipolar/Unipolar Bit. A 0 in this bit selects bipolar operation and the output coding is 00. . . 000 for
negative full-scale input, 10 . . . 000 for zero input, and 11 . . . 111 for positive full-scale input. A 1 in
this bit selects unipolar operation and the output coding is 00 . . . 000 for zero input and 11 . . . 111 for
positive full-scale input.
MR11 DEN Digital Output Enable Bit. With this bit at 1, the AIN2(+)/D1 and AIN2(–)/D0 pins assume their
digital output functions and the output drivers connected to these pins are enabled. In this mode, the
user effectively has two port bits which can be programmed over the serial interface.
MR10–MR9 D1–D0 Digital Output Bits. These bits determine the digital outputs on the AIN2(+)/D1 and AIN2(–)/D0 pins,
respectively, when the DEN bit is a 1. For example, a 1 written to the D1 bit of the Mode Register
(with the DEN bit also a 1) will put a logic 1 on the AIN2(+)/D1 pin. This logic 1 will remain on this
pin until a 0 is written to the D1 bit (in which case the AIN2(+)/D1 pin goes to a logic 0) or the digital
output function is disabled by writing a 0 to the DEN bit.
MR8 WL Data Word Length Bit. This bit determines the word length of the Data Register. A 0 in this bit selects
16-bit word length when reading from the data register (i.e., RDY returns high after 16 serial clock
cycles in the read operation). A 1 in this bit selects 24-bit word length for the Data Register.
MR7 HIREF High Reference Bit. This bit should be set in accordance with the reference voltage which is being used
on the part. If the reference voltage is 5 V, the HIREF bit should be set to 1. If the reference voltage is
2.5 V, the HIREF bit should be set to a 0. With the HIREF bit set correctly for the appropriate applied
reference voltage, the input ranges are 0 mV to +10 mV, +20 mV, +40 mV and +80 mV for unipolar
operation and ± 10 mV, ± 20 mV, ± 40 mV and ±80 mV for bipolar operation.
It is possible for a user with a 2.5 V reference to set the HIREF bit to a 1. In this case, the part is oper-
ating with a 2.5 V reference but assumes it has a 5 V reference. As a result, the input ranges on the part
become 0 to +5 mV, +10 mV, +20 mV and +40 mV for unipolar operation and ± 5 mV, ± 10 mV,
± 20 mV and ±40 mV for bipolar operation. However, the output noise from the part (in nV) will re-
main unchanged so the resolution of the part (in counts) will halve.
MR6 ZERO A zero must be written to this bit to ensure correct operation of the AD7730.
MR5–MR4 RN1–RN0 Input Range Bits. These bits determine the analog input range for the selected analog input. The dif-
ferent input ranges are outlined in Table XII. The table is valid for a reference voltage of 5 V with the
HIREF bit at 1, or for a reference voltage of 2.5 V with the HIREF bit at a logic 0.
Table XII. Input Range Selection
RN1 RN0 B/U Bit = 0 B/U Bit = 1
0 0 –10 mV to +10 mV 0 mV to +10 mV
0 1 –20 mV to +20 mV 0 mV to +20 mV
1 0 –40 mV to +40 mV 0 mV to +40 mV
1 1 –80 mV to +80 mV 0 mV to +80 mV Power-On/Reset Default
Note that the input range given in the above table is the range that appears at the input of the PGA
after the DAC offset value has been applied. If the DAC adjusts out no offset (DAC Register is 0010
0000), then this is also the input voltage range at the analog input pins. If, for example, the DAC sub-
tracts out 50 mV of offset and the part is being operated in bipolar mode with RN1 and RN0 at 0, 0,
the actual input voltage range at the analog input is +40 mV to +60 mV.
MR3 CLKDIS Master Clock Disable Bit. A 1 in the bit disables the master clock from appearing at the MCLK OUT
pin. When disabled, the MCLK OUT pin is forced low. It allows the user the flexibility of using the
MCLK OUT as a clock source for other devices in the system or of turning off the MCLK OUT as a
power saving feature. When using an external master clock at the MCLK IN pin, the AD7730 contin-
ues to have internal clocks and will convert normally with the CLKDIS bit active. When using a crystal
oscillator or ceramic resonator across the MCLK IN and MCLK OUT pins, the AD7730 clock is
stopped and no conversions take place when the CLKDIS bit is active.