Datasheet

AD7798/AD7799 Data Sheet
Rev. B | Page 20 of 28
Single-Conversion Mode
In single-conversion mode, the AD7798/AD7799 is placed in
power-down mode after conversions. When a single conversion
is initiated by setting MD2, MD1, and MD0 to 0, 0, and 1 in the
mode register, the AD7798/AD7799 powers up, performs a
single conversion, and then returns to power-down mode. The
on-chip oscillator requires approximately 1 ms to power up. A
conversion requires a time period of 2 × t
ADC
. DOUT/
RDY
goes
low to indicate the completion of a conversion. When the data-
word has been read from the data register, DOUT/
RDY
goes
high. If
CS
is low, DOUT/
RDY
remains high until another
conversion is initiated and completed. The data register can be
read several times if required, even when DOUT/
RDY
is high.
Continuous-Conversion Mode
This is the default power-up mode. The AD7798/AD7799
continuously converts, with the
RDY
bit in the status register
going low each time a conversion is complete. If
CS
is low, the
DOUT/
RDY
line also goes low when a conversion is complete.
To read a conversion, the user can write to the communication
register, indicating that the next operation is a read of the data
register. The digital conversion is placed on the DOUT/
RDY
pin as soon as SCLK pulses are applied to the ADC. DOUT/
RDY
returns high when the conversion is read. The user can reread
this register if required. However, the user must ensure that the
data register is not accessed at the completion of the next
conversion, or the new conversion word is lost.
04856-017
DIN
0x08
0x200A
DATA
SCLK
DOUT/RDY
CS
0x58
Figure 16. Single Conversion
04856-018
DIN
SCLK
DOUT/RDY
CS
0x58
0x58
DATA DATA
Figure 17. Continuous Conversion