Book Analog Interfacing to Embedded Microprocessors
Finally, it is possible to generate an interrupt to the microcontroller when
the ADC conversion is complete. An extra connection is shown in Figure 2.15,
from the MAX1242 DOUT pin to an interrupt on the microcontroller. When
-CS is low and the conversion is completed, DOUT will go high, interrupt-
ing the microcontroller. To use this method, the firmware must ignore the
interrupt except when a conversion is in process.
Another ADC with an SPI-compatible interface is the Analog Devices
AD7823. Like the MAX1242, the AD7823 uses 3 pins: SCLK, DOUT, and
-CONVST. The AD7823 is an 8-bit successive approximation ADC with inter-
Digital-to-Analog Converters 37
Figure 2.15
Maxim MAX1242 interface.
nal S/H. A conversion is started on the falling edge of -CONVST, and takes
5.5 ms. The rising edge of -CONVST enables the serial interface.
Unlike the MAX1242, the AD7823 does not drive the data pin until the
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