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100 lines
4.3 KiB
Markdown
100 lines
4.3 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/PCF8574/blob/master/LICENSE)
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[](https://github.com/RobTillaart/PCF8574/releases)
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# PCF8574
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Arduino library for PCF8574 - 8 channel I2C IO expander
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## Description
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Related to the PCF8575 16 channel IO expander library https://github.com/RobTillaart/PCF8575
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This library gives easy control over the 8 pins of a PCF8574 and PCF8574A chip.
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These chips are identical in behavior although there are two distinct address ranges.
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| TYPE | ADDRESS-RANGE | notes |
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|:---------|:-------------:|:------------------------:|
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|PCF8574 | 0x20 to 0x27 | same range as PCF8575 !! |
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|PCF8574A | 0x38 to 0x3F | |
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So you can connect up to 16 PCF8574 on one I2C bus, giving access
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to 16 x 8 = 128 IO lines. To maximize IO lines combine 8 x PCF8575 + 8 x PCF8574A giving
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128 + 64 = 192 IO lines. Be sure to have a well dimensioned power supply.
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The library allows to read and write both single pins or 8 pins at once.
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Furthermore some additional functions are implemented that are
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playful but useful.
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## Interface
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**PCF8574_INITIAL_VALUE** is a define that can be set compile time or before
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the include of "pcf8574.h" to overrule the default value used with the
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**begin()** call.
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### Constructor
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- **PCF8574(deviceAddress, TwoWire \*wire = &Wire)** Constructor with device address,
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and optional the Wire interface as parameter.
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- **bool begin(val = PCF8574_INITIAL_VALUE)** set the initial value for the pins and masks.
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- **bool begin(sda, scl, val = PCF8574_INITIAL_VALUE)** idem, for the ESP32 where one can choose the I2C pins.
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- **bool isConnected()** checks if the address set in the constructor or by **setAddress()** is visible on the I2C bus.
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- **bool setAddress(const uint8_t deviceAddress)** sets the device address after construction. Can be used to switch between PCF8574 modules runtime. Note this corrupts internal buffered values, so one might need to call **read8()** and/or **write8()**. Returns true if address can be found on I2C bus.
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- **uint8_t getAddress()** returns the device address.
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### Read and Write
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- **uint8_t read8()** reads all 8 pins at once. This one does the actual reading.
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- **uint8_t read(uint8_t pin)** reads a single pin; pin = 0..7
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- **uint8_t value()** returns the last read inputs again, as this information is buffered
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in the class this is faster than reread the pins.
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- **void write8(const uint8_t value)** writes all 8 pins at once. This one does the actual reading.
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- **uint8_t write(const uint8_t pin, const uint8_t value)** writes a single pin; pin = 0..7; value is HIGH(1) or LOW (0)
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- **valueOut()** returns the last written data.
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### Button
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- **void setButtonMask(const uint8_t mask)**
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- **uint8_t readButton8()**
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- **uint8_t readButton8(const uint8_t mask)**
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- **uint8_t readButton(const uint8_t pin)**
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### Special
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- **void toggle(const uint8_t pin)** toggles a single pin
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- **void toggleMask(const uint8_t mask = 0xFF)** toggles a selection of pins,
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if you want to invert all pins use 0xFF (default value).
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- **void shiftRight(const uint8_t n = 1)** shifts output channels n pins (default 1) pins right (e.g. leds ).
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Fills the higher lines with zero's.
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- **void shiftLeft(const uint8_t n = 1)** shifts output channels n pins (default 1) pins left (e.g. leds ).
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Fills the lower lines with zero's.
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- **void rotateRight(const uint8_t n = 1)** rotates output channels to right, moving lowest line to highest line.
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- **void rotateLeft(const uint8_t n = 1)** rotates output channels to left, moving highest line to lowest line.
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- **void reverse()** revers the "bit pattern" of the lines, high to low and vice versa.
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### Misc
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- **int lastError()** returns the last error from the lib. (see .h file)
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## Error codes
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| name | value | description |
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|:-------------------|:-----:|:------------------------|
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| PCF8574_OK | 0x00 | no error |
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| PCF8574_PIN_ERROR | 0x81 | pin number out of range |
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| PCF8574_I2C_ERROR | 0x82 | I2C communication error |
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## Operation
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See examples
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