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1

2

3

6

8

7

10

9

DAC7574

GND

A1

A0

SDA

SCL

GPIO-2

GPIO-1

Microcontroller or

Microprocessor

4

5

DAC7574

SLAS375 – JUNE 2003

APPLICATION INFORMATION (continued)

Figure 41. Using GPIO With a Single DAC7574

output modes to apply the proper bus states. To drive the line low, the pin is set to output a zero; to let the line

go high, the pin is set to input. When the pin is set to input, the state of the pin can be read; if another device is

pulling the line low, this reads as a zero in the port’s input register.

Note that no pullup resistor is shown on the SCL line. In this simple case the resistor is not needed. The

microcontroller can simply leave the line on output, and set it to one or zero as appropriate. It can do this

because the DAC7574 never drives its clock line low. This technique can also be used with multiple devices, and

has the advantage of lower current consumption due to the absence of a resistive pullup.

If there are any devices on the bus that may drive their clock lines low, the above method should not be used.

The SCL line should be high-Z or zero, and a pullup resistor provided as usual. Note also that this cannot be

devices do.

Some microcontrollers have selectable strong pullup circuits built in to their GPIO ports. In some cases, these

can be switched on and used in place of an external pullup resistor. Weak pullups are also provided on some

production.

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