Book Analog Interfacing to Embedded Microprocessors
operating in the older system, but older peripherals are not useable in a
higher-speed system. The faster interfaces have some limitations, such as the
need for active pullups and limits on bus capacitance. Of course, the faster
modes of operation require hardware support and are not suitable for a
software-controlled implementation.
Figure 2.16
I2C timing.
Digital-to-Analog Converters 39
A typical ADC using I2C is the Philips PCF8591. This part includes both an
ADC and a DAC. Like many I2C devices, the 8591 has three pins: A0, A1, and
A2. These can be connected to either “1” or “0” to select which address the
device responds to. When the peripheral address is decoded, the PCF8591 will
respond to address 1001xxx, where xxx matches the value of the A2, A1, and
A0 pins. This allows up to eight PCF8591 devices to share a single I2C bus.
Proprietary Serial Interfaces
Some ADCs have a proprietary interface
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