AD7194 Analog Devices, AD7194 Datasheet - Page 19

• Manufacturer Part Number: AD7194
• Description: 8-Channel, 4.8 kHz, Ultralow Noise, 24-Bit Sigma-Delta ADC with PGA
• Manufacturer: Analog Devices

Specifications of AD7194

• Resolution (bits): 24bit
• # Chan: 8
• Sample Rate: n/a
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (2Vref/PGA Gain) p-p
• Adc Architecture: Sigma-Delta
• Pkg Type: CSP

COMMUNICATIONS REGISTER
RS2, RS1, RS0 = 000
The communications register is an 8-bit write-only register. All
communications to the part must start with a write operation to
the communications register. The data written to the communi-
cations register determine whether the next operation is a read
or write operation and in which register this operation occurs. For
read or write operations, when the subsequent read or write oper-
ation to the selected register is complete, the interface returns to
where it expects a write operation to the communications register.
This is the default state of the interface and, on power-up or after
CR7
WEN(0)
Table 16. Communications Register (CR) Bit Designations
Bit Location
CR7
CR6
CR5 to CR3
CR2
CR1 to CR0
Table 17. Register Selection
RS2
0
0
0
0
0
1
1
1
1
RS1
0
0
0
1
1
0
0
1
1
CR6
R/W(0)
Bit Name
WEN
R/W
RS2 to RS0
CREAD
0
RS0
0
0
1
0
1
0
1
0
1
Description
Write enable bit. For a write to the communications register to occur, 0 must be written to this bit. If a 1 is
the first bit written, the part does not clock onto subsequent bits in the register; rather, it stays at this bit
location until a 0 is written to this bit. After a 0 is written to the WEN bit, the next seven bits are loaded to
the communications register. Idling the DIN pin high between data transfers minimizes the effects of
spurious SCLK pulses on the serial interface.
0 in this bit location indicates that the next operation is a write to a specified register.
1 in this bit position indicates that the next operation is a read from the designated register.
Register address bits. These address bits are used to select which registers of the ADC are selected during
the serial interface communication (see Table 17).
Continuous read of the data register. When this bit is set to 1 (and the data register is selected), the serial
interface is configured so that the data register can be continuously read; that is, the contents of the data
register are automatically placed on the DOUT pin when the SCLK pulses are applied after the RDY pin
goes low to indicate that a conversion is complete. The communications register does not have to be
written to for subsequent data reads. To enable continuous read, Instruction 01011100 must be written to
the communications register. To disable continuous read, Instruction 01011000 must be written to the
communications register while the RDY pin is low. While continuous read is enabled, the ADC monitors
activity on the DIN line so that it can receive the instruction to disable continuous read. Additionally, a
reset occurs if 40 consecutive 1s occur on DIN; therefore, hold DIN low until an instruction is written to
the device.
These bits must be programmed to Logic 0 for correct operation.
Register
Communications register during a write operation
Status register during a read operation
Mode register
Configuration register
Data register/data register plus status information
ID register
GPOCON register
Offset register
Full-scale register
CR5
RS2(0)
CR4
RS1(0)
Rev. 0 | Page 19 of 56
CR3
RS0(0)
a reset, the ADC is in this default state waiting for a write
operation to the communications register. In situations where the
interface sequence is lost, a write operation of at least 40 serial
clock cycles with DIN high returns the ADC to this default state
by resetting the entire part. Table 16 outlines the bit designations
for the communications register. CR0 through CR7 indicate the
bit location, CR denoting that the bits are in the communications
register. CR7 denotes the first bit of the data stream. The number
in parentheses indicates the power-on/reset default status of
that bit.
CR2
CREAD(0)
CR1
0(0)
Register Size
8 bits
8 bits
24 bits
24 bits
24 bits/32 bits
8 bits
8 bits
24 bits
24 bits
CR0
0(0)
AD7194