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198 lines
7.6 KiB
Markdown
198 lines
7.6 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/PCF8574/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/PCF8574/actions/workflows/jsoncheck.yml)
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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 behaviour 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.
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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 playful and useful.
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#### Interrupts
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The PCF8574 has an interrupt output line (INT) to notify an MCU that one of the input lines has changed.
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This can be used to prevent active polling of the PCF8574, which can be more efficient.
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The library cannot handle the PCF8574 interrupts as it has no code for it.
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The user should catch the interrupt in his own code and can use the library to see which line has changed.
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There are two examples to show how interrupts can be used:
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- PCF8574_interrupt.ino
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- PCF8574_rotaryEncoder.ino
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#### Related
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16 bit port expanders
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- https://github.com/RobTillaart/MCP23017_RT
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- https://github.com/RobTillaart/MCP23S17
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- https://github.com/RobTillaart/PCF8575
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8 bit port expanders
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- https://github.com/RobTillaart/MCP23008
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- https://github.com/RobTillaart/MCP23S08
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- https://github.com/RobTillaart/PCF8574
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## I2C Clock
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Tested on UNO with **PCF8574_performance** showed that the PCF8574 still works at 500 KHz and failed at 600 KHz.
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These values are outside the specs of the datasheet so they are not recommended.
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However when performance is needed you can try to overclock the chip.
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| clock speed | Read | Write | Notes |
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|:-----------:|:------:|:-------:|:--------------------|
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| 100000 | 236 | 240 | spec datasheet |
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| 200000 | 132 | 140 |
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| 300000 | 104 | 108 |
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| 400000 | 96 | 96 | max advised speed |
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| 500000 | 92 | 92 | not recommended |
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| 600000 | crash | crash |
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## Interface
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```cpp
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#include "PCF8574.h"
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```
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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 **begin()** call.
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### Constructor
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- **PCF8574(uint8_t deviceAddress = 0x20, TwoWire \*wire = &Wire)** Constructor with optional device address, default 0x20,
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and the optional Wire interface as parameter.
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- **bool begin(uint8_t value = PCF8574_INITIAL_VALUE)** set the initial value for the pins and masks.
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- **bool begin(int sda, int scl, uint8_t value = 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.
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Can be used to switch between PCF8574 modules runtime. Note this corrupts internal buffered values,
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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 writing.
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- **uint8_t write(const uint8_t pin, const uint8_t value)** writes a single pin; pin = 0..7;
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value is HIGH(1) or LOW (0)
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- **uint8_t valueOut()** returns the last written data.
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### Button
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The **"button"** functions are to be used when you mix input and output on one IC.
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It does not change / affect the pins used for output by masking these.
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Typical usage is to call **setButtonMask()** once in setup as pins do not (often) change
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during program execution.
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- **void setButtonMask(const uint8_t mask)** sets the (bit) mask which lines are input.
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- **uint8_t getButtonMask()** returns the set buttonMask.
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- **uint8_t readButton8()** use the mask set by setButtonMask to select specific input pins.
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- **uint8_t readButton8(const uint8_t mask)** use a specific mask to select specific input pins.
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Note this can be a subset of the pins set with **setButtonMask()** if one wants to process not all.
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- **uint8_t readButton(const uint8_t pin)** read a singe input pin.
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Background - https://github.com/RobTillaart/Arduino/issues/38
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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()** reverse the "bit pattern" of the lines, swapping pin 7 with 0, 6 with 1, 5 with 2 etc.
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### Select
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Some convenience wrappers.
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- **void select(const uint8_t pin)** sets a single pin to HIGH, all others are set to LOW.
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If pin > 7 all pins are set to LOW.
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Can be used to select one of n devices.
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- **void selectN(const uint8_t pin)** sets pins 0..pin to HIGH, all others are set to LOW.
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If pin > 7 all pins are set to LOW.
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This can typical be used to implement a VU meter.
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- **void selectNone()** sets all pins to LOW.
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- **void selectAll()** sets all pins to HIGH.
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### Miscellaneous
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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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It is advised to use pull-up or pull-down resistors so the lines have a defined state at startup.
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## Future
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#### Must
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- keep in sync with PCF8575
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#### Should
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#### Could
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- move code to .cpp
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#### Wont
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