DAC8574IPWR datasheet(30/46 Pages) TI2

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DAC8574

VOUTA

VOUTB

VREFH

VDD

VREFL

GND

VOUTC

VOUTD

IOVDD

SDA

SCL

LDAC

GPIO-2

GPIO-1

IOVDD

Microcontroller or

Microprocessor

NOTE: DAC8574 power and input/output connections are omitted for clarity, except I2C Inputs.

DAC8574

SLAS377B – JANUARY 2003 – REVISED DECEMBER 2004

APPLICATION INFORMATION (continued)

Figure 57. Using GPIO With a Single DAC8574

Bit-banging I

2C with GPIO pins can be done by setting the GPIO line to zero and toggling it between input and

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 DAC8574 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

done on the SDA line in any case, because the DAC8574 drives the SDA line low from time to time, as all I

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

microcontrollers, but usually these are too weak for I

2C communication. Test any circuit before committing it to

production.

DAC8574IPWR Datasheet(PDF) 30 Page - Texas Instruments

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