AD7851 Analog Devices, AD7851 Datasheet - Page 10

• Manufacturer Part Number: AD7851
• Description: 14-Bit, 333 kSPS, Serial Sampling A/D Converter
• Manufacturer: Analog Devices

Specifications of AD7851

• Resolution (bits): 14bit
• # Chan: 1
• Sample Rate: 333kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (Vref) p-p,Uni (Vref)
• Adc Architecture: SAR
• Pkg Type: DIP,SOIC,SOP

AD7851
AD7851 ON-CHIP REGISTERS
The AD7851 powers up with a set of default conditions, and the user need not ever write to the device. In this case, the AD7851 will
operate as a read-only ADC. The AD7851 still retains the flexibility for performing a full power-down and a full self-calibration.
Note that the DIN pin should be tied to DGND for operating the AD7851 as a read-only ADC.
Extra features and flexibility, such as performing different power-down options, different types of calibrations, including system cali-
bration, and software conversion starts can be selected by writing to the part.
The AD7851 contains a control register, ADC output data register, status register, test register, and 10 calibration registers.
The control register is write-only, the ADC output data register and the status register are read-only, and the test and calibration
registers are both read/write registers. The test register is used for testing the part and should not be written to.
Addressing the On-Chip Registers
Writing
A write operation to the AD7851 consists of 16 bits. The two MSBs, ADDR0 and ADDR1, are decoded to determine which regis-
ter is addressed, and the subsequent 14 bits of data are written to the addressed register. It is not until all 16 bits are written that
the data is latched into the addressed register. Table I shows the decoding of the address bits, while Figure 4 shows the overall
write register hierarchy.
ADDR1
0
0
1
1
Reading
To read from the various registers the user must first write to Bits 6 and 7 in the Control Register, RDSLT0 and RDSLT1. These
bits are decoded to determine which register is addressed during a read operation. Table II shows the decoding of the read address
bits while Figure 5 shows the overall read register hierarchy. The power-up status of these bits is 00 so that the default read will be
from the ADC output data register.
Once the read selection bits are set in the control register, all subsequent read operations that follow will be from the selected register
until the read selection bits are changed in the control register.
RDSLT1
0
0
1
1
Figure 4. Write Register Hierarchy/Address Decoding
CALSLT1, CALSLT0
DECODE
RDSLT0
0
1
0
1
ADDR0
0
1
0
1
OFFSET (1)
GAIN (1)
00
REGISTER
DAC (8)
01
Comment
This combination does not address any register so the subsequent 14 data bits are ignored.
This combination addresses the TEST REGISTER. The subsequent 14 data bits are written to the test register.
This combination addresses the CALIBRATION REGISTERS. The subsequent 14 data bits are written
to the selected calibration register.
This combination addresses the CONTROL REGISTER. The subsequent 14 data bits are written to the
control register.
Comment
All successive read operations will be from ADC OUTPUT DATA REGISTER. This is the power-up default
setting. There will always be two leading zeros when reading from the ADC output data register.
All successive read operations will be from TEST REGISTER.
All successive read operations will be from CALIBRATION REGISTERS.
All successive read operations will be from STATUS REGISTER.
TEST
OFFSET (1)
GAIN (1)
01
ADDR1, ADDR0
CALIBRATION
REGISTERS
DECODE
10
OFFSET (1)
10
Table II. Read Register Addressing
Table I. Write Register Addressing
CONTROL
REGISTER
GAIN (1)
11
11
–10–
Figure 5. Read Register Hierarchy/Address Decoding
CALSLT1, CALSLT0
DATA REGISTER
ADC OUTPUT
DECODE
00
OFFSET (1)
00
GAIN (1)
REGISTER
DAC (8)
01
TEST
OFFSET (1)
GAIN (1)
01
RDSLT1, RDSLT0
CALIBRATION
REGISTERS
DECODE
10
OFFSET (1)
10
REGISTER
STATUS
GAIN (1)
11
11
REV. B