Pin 14 is for the I2C clock input (Connect to VCC through a pull-up resistor). Pin 15 is for the I2C serial data input or output (Connect to VCC through a pull-up resistor) and.At power on, all these I/O pins are at HIGH state. Each of these bidirectional I/O pins can be used as an input or output without the use of a data-direction control signal. Pins 4~7 and 9~12 are the P0 to P7 8-Parallel (which means you can use all the 8 pins at once) I/O pins.Pin 16 of this IC is VCC which can operate on 2.5V to 6V.Lets first checkout the pin-outs of the PCF8574 IC: at the max 8 of these devices can be connected in a project to the I2C bus. The Address range of PCF8574 is from 0x20 to 0x27 (7 bit address mode). PCF8574 GPIO Extender run on the I2C bus, extending the 'IO Pins' which can be controlled by a single host I2C bus. Both masters and slaves can transmit or receive data. Usually there is one master and one or multiple slaves on the line, however there can be multiple masters aswell. The two wires are:īoth of these lines are open-drain, and are pulled-up with resistors. For now we will just cover the basics of I2C and we will jump to our main topic. If you want to know more about the I2C technology please check out my 'Tutorial Number 09'. Inter-integrated Circuit pronounced I-squared-C (I☬) or I2C is a 'short distance', 'two wire bus technology' (well actually 4 wires because you also need the VCC and Ground) that is used for 'serial communication' between multiple processors and sensors. You just need to hook them up to the I2C bus and you are all ready to go. If you don't want to worry about the wiring and just want to keep your project really "simple", then you can buy these fully assembled breakout boards. These ICs are ridiculously cheap and can be bought easily from eBay or AliExpress. Each device will give us an additional 8-bits of GPIO enabling 64 GPIOs in total. These modules run on the I2C bus, and if daisy-chained you can connect upto 8 of these devices in a project. This "GPIO (General Purpose Input Output) pin extender" provides an additional 8 pins (P0 ~ P7) which can be used to 'output a signal' or 'read a signal as an input'. This tiny little board becomes a life saver When you run out of pins on your Arduino. It is one of the many GPIO extenders available in the market. In this tutorial, I am going to talk about the PCF8574 8-bit GPIO Port Extender. In my last tutorial, I talked about the TCA9548A MUX which can be used to add at the max of 64 I2C or I☬ sensors to your Arduino/ESP8266/ESP32.
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