REV. G
–24–
AD7710
SIMPLIFYING THE EXTERNAL CLOCKING MODE
INTERFACE
In many applications, the user may not need to write to the on-chip
calibration registers. In this case, the serial interface to the AD7710
in external clocking mode can be simplified by connecting the TFS
line to the A0 input of the AD7710 (see Figure 14). This means
that any write to the device will load data to the control register
(because A0 is low while TFS is low), and any read to the de-
vice will access data from the output data register or from the
calibration registers (because A0 is high while RFS is low). Note
that in this arrangement the user does not have the capability of
reading from the control register.
AD7710
SDATA
SCLK
TFS
A0
FOUR
INTERFACE
LINES
RFS
Figure 14. Simplified Interface with
TFS
Connected to A0
Another method of simplifying the interface is to generate the
TFS signal from an inverted RFS signal. However, generating
the signals the opposite way around (RFS from an inverted
TFS) will cause writing errors.
MICROCOMPUTER/MICROPROCESSOR INTERFACING
The AD7710’s flexible serial interface allows for easy interface
to most microcomputers and microprocessors. Figure 15 shows
a flowchart for a typical programming sequence for reading data
from the AD7710 to a microcomputer, while Figure 16 shows a
flowchart for writing data to the AD7710. Figures 17, 18, and
19 show some typical interface circuits.
Figure 15 shows continuous read operations from the AD7710
output register, where the DRDY line is continuously polled.
Depending on the microprocessor configuration, the DRDY line
may come to an interrupt input, in which case the DRDY will
automatically generate an interrupt without being polled. Read-
ing the serial buffer could be anything from one read operation
up to three read operations (where 24 bits of data are read into
an 8-bit serial register). A read operation to the control/calibra-
tion registers is similar, but, in this case, the status of DRDY
can be ignored. The A0 line is brought low when the RFS line
is brought low during a read register.
The flowchart also shows the bits being reversed after they have
been read in from the serial port. This depends on whether the
microprocessor expects the MSB of the word first or the LSB of
the word first. The AD7710 outputs the MSB first.
Figure 16 shows a single 24-bit write operation to the AD7710
control or calibration registers. This shows data being trans-
ferred from data memory to the accumulator before being writ-
ten to the serial buffer. Some microprocessor systems allow data
to be written directly to the serial buffer from data memory.
Writing data to the serial buffer from the accumulator generally
consists of either two or three write operations, depending on
the size of the serial buffer.
NO
YES
BRING
RFS LOW
ⴛ3
REVERSE
ORDER OF BITS
BRING
RFS HIGH
POLL DRDY
CONFIGURE AND
INITIALIZE C/P
SERIAL PORT
DRDY
LOW?
BRING
RFS, TFS HIGH
START
READ
SERIAL BUFFER
Figure 15. Flowchart for Continuous Read Operations
to the AD7710
Figure 16 also shows the option of the bits being reversed before
being written to the serial buffer. This depends on whether the
first bit transmitted by the microprocessor is the MSB or the
LSB. The AD7710 expects the MSB as the first bit in the data
stream. In cases where the data is being read or being written in
bytes and the data has to be reversed, the bits have to be reversed
for every byte.
