Datasheet

AD7854/AD7854L
REV. B
9
CONTROL REGISTER
The arrangement of the control register is shown below. The control register is a write only register and contains 14 bits of data. The
control register is selected by putting two 1s in ADDR1 and ADDR0. The function of the bits in the control register is described
below. The power-up status of all bits is 0.
MSB
ZERO ZERO ZERO ZERO PMGT1 PMGT0 RDSLT1
RDSLT0 AMODE CONVST CALMD CALSLT1 CALSLT0 STCAL
LSB
Control Register Bit Function Description
Bit Mnemonic Comment
13 ZERO These four bits must be set to 0 when writing to the control register.
12 ZERO
11 ZERO
10 ZERO
9 PMGT1 Power Management Bits. These two bits are used for putting the part into various power-down modes
8 PMGT0 (See Power-Down section for more details).
7 RDSLT1 Theses two bits determine which register is addressed for the read operations. See Table II.
6 RDSLT0
5 AMODE Analog Mode Bit. This pin allows two different analog input ranges to be selected. A logic 0 in this bit
position selects range 0 to V
REF
(i.e., AIN(+) AIN() = 0 to V
REF
). In this range AIN(+) cannot go
below AIN() and AIN() cannot go below AGND and data coding is straight binary. A logic 1 in this
bit position selects range V
REF
/2 to +V
REF
/2 (i.e., AIN(+) AIN() = V
REF
/2 to +V
REF
/2). AIN(+)
cannot go below AGND, so for this range, AIN() needs to be biased to at least +V
REF
/2 to allow
AIN(+) to go as low as AIN() V
REF
/2 V. Data coding is twos complement for this range.
4 CONVST Conversion Start Bit. A logic one in this bit position starts a single conversion, and this bit is automati-
cally reset to 0 at the end of conversion. This bit may also used in conjunction with system calibration
(see Calibration section).
3 CALMD Calibration Mode Bit. A 0 here selects self-calibration and a 1 selects a system calibration (see Table III).
2 CALSLT1 Calibration Selection Bits and Start Calibration Bit. These bits have two functions.
1 CALSLT0 With the STCAL bit set to 1, the CALSLT1 and CALSLT0 bits determine the type of calibration per-
0 STCAL formed by the part (see Table III). The STCAL bit is automatically reset to 0 at the end of calibration.
With the STCAL bit set to 0, the CALSLT1 and CALSLT0 bits are decoded to address the calibration
register for read/write of calibration coefficients (see section on the calibration registers for more details).
Table III. Calibration Selection
CALMD CALSLT1 CALSLT0 Calibration Type
00 0 A full internal calibration is initiated. First the internal DAC is calibrated, then the
internal gain error and finally the internal offset error are removed. This is the default setting.
0 0 1 First the internal gain error is removed, then the internal offset error is removed.
0 1 0 The internal offset error only is calibrated out.
0 1 1 The internal gain error only is calibrated out.
10 0 A full system calibration is initiated. First the internal DAC is calibrated, followed by the
system gain error calibration, and finally the system offset error calibration.
1 0 1 First the system gain error is calibrated out followed by the system offset error.
1 1 0 The system offset error only is removed.
1 1 1 The system gain error only is removed.