Communications Register - Analog Devices AD7195 Manual

AD7195

COMMUNICATIONS REGISTER

(RS2, RS1, RS0 = 0, 0, 0)
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 communications register determines whether the next
operation is a read or a write operation and in which register
this operation takes place. For read or write operations, when
the subsequent read or write operation to the selected register
is complete, the interface returns to where it expects a write
operation to the communications register. This is the default
CR7 CR6
WEN(0) R/W(0)
Table 19. Communications Register Bit Designations
Bit Location Bit Name
CR7 WEN
CR6 R/W
CR5 to CR3 RS2 to RS0
CR2 CREAD
CR1 to CR0 0
Table 20. Register Selection
RS2 RS1 RS0
0 0 0
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1
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CR5 CR4
RS2(0) RS1(0)
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 on to 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.
A 0 in this bit location indicates that the next operation is a write to a specified register. A 1 in this 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 20).
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, the Instruction 01011100 must be written
to the communications register. To disable continuous read, the 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 are seen 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
Rev. 0 | Page 18 of 44
state of the interface and, on power-up or after 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 19 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.
CR3 CR2
RS0(0) CREAD(0)
CR1 CR0
0 0
Register Size
8 bits
8 bits
24 bits
24 bits
24 bits/32 bits
8 bits
8 bits
24 bits
24 bits