Datasheet

Data Sheet AD5780
Rev. E | Page 21 of 28
Control Register
The control register controls the mode of operation of the
AD5780.
Clearcode Register
The clearcode register sets the value to which the DAC output is
set when the
CLR
pin or CLR bit in the software control register
is asserted. The output value depends on the DAC coding that is
being used, either binary or twos complement. The default
register value is 0.
Table 10. Control Register
MSB
LSB
DB23 DB22 DB21 DB20 DB19 to DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
R/
W
Register address Control register data
R/
W
0 1 0 Reserved Reserved 0000 SDODIS BIN/2sC DACTRI OPGND RBUF Reserved
Table 11. Control Register Functions
Bit Name Description
Reserved These bits are reserved and should be programmed to zero.
RBUF Output amplifier configuration control.
0: the internal amplifier, A1, is powered up and Resistors R
FB
and R1 are connected in series as shown in Figure 52. This allows
an external amplifier to be connected in a gain of two configuration. See the AD5780 Features section for further details.
1: (default) the internal amplifier, A1, is powered down and Resistors R
FB
and R1 are connected in parallel, as shown in Figure 51,
so that the resistance between the R
FB
and INV pins is 3.4 kΩ, equal to the resistance of the DAC. This allows the R
FB
and INV
pins to be used for input bias current compensation for an external unity-gain amplifier. See the AD5780 Features section for
further details.
OPGND Output ground clamp control.
0: the DAC output clamp to ground is removed, and the DAC is placed in normal mode.
1: (default) the DAC output is clamped to ground through a ~6 kΩ resistance, and the DAC is placed in tristate mode.
Resetting the
part puts the DAC in OPGND mode, where the output ground clamp is enabled and the DAC is tristated. Setting
the OPGND bit to 1 in the control register overrules any write to the DACTRI bit
DACTRI DAC tristate control.
0: the DAC is in normal operating mode.
1: (default) the DAC is in tristate mode.
BIN/2sC DAC register coding selection.
0: (default) the DAC register uses twos complement coding.
1: the DAC register uses offset binary coding.
SDODIS SDO pin enable/disable control.
0: (default) the SDO pin is enabled.
1: the SDO pin is disabled (tristate).
R/
W
Read/write select bit.
0: AD5780 is addressed for a write operation.
1: AD5780 is addressed for a read operation.
Table 12. Clearcode Register
MSB LSB
DB23 DB22 DB21 DB20 DB19 to DB2 DB1 DB0
R/
W
Register address Clearcode register data
R/
W
0 1 1 18 bits of data X
1
X
1
1
X is don’t care.