Datasheet

AD7788/AD7789
Rev. B | Page 16 of 20
Continuous Read Mode
Rather than write to the communications register each time a
conversion is complete to access the data, the AD7788/AD7789
can be placed in continuous read mode. By writing 001111XX
to the communications register, the user needs only to apply the
appropriate number of SCLK cycles to the ADC and the data-
word is automatically placed on the DOUT/
RDY
line when a
conversion is complete.
When DOUT/
RDY
goes low to indicate the end of a conver-
sion, sufficient SCLK cycles must be applied to the ADC and
the data conversion is placed on the DOUT/
RDY
line. When
the conversion is read, DOUT/
RDY
returns high until the next
conversion is available. In this mode, the data can be read only
once. Also, the user must ensure that the data-word is read
before the next conversion is complete.
If the data-word has not read the conversion before the
completion of the next conversion, or if insufficient serial clocks
are applied to the AD7788/AD7789 to read the word, the serial
output register is reset when the next conversion is complete
and the new conversion is placed in the output serial register.
To exit continuous read mode, the instruction 001110XX must
be written to the communications register while the DOUT/
RDY
pin is low. While in continuous read mode, the ADC
monitors activity on the DIN line so that it can receive the
instruction to exit continuous read mode. Additionally, a
reset occurs if 32 consecutive 1s are seen on DIN. Therefore,
DIN should be held low in continuous read mode until an
instruction is to be written to the device.
03539-011
DIN
SCLK
DOUT/RD
Y
CS
0x3C
DATA DATA DATA
Figure 13. Continuous-Read Mode