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# MCP23S17

Arduino library for MCP23S17 16 channel SPI port expander.


## Description

This experimental library gives easy control over the 16 pins of a (SPI) MCP23S17 chip.

This IC is strongly related to the MCP23017 I2C port expander - https://github.com/RobTillaart/MCP23017_RT
Programming Interface is kept the same as much as possible.


## Interface

### Constructor

- **MCP23S17(uint8_t select, uint8_t dataIn, uint8_t dataOut, uint8_t clock, uint8_t address = 0x00)** constructor SW SPI.
- **MCP23S17(uint8_t select, SPIClass\* spi)** constructor HW SPI with explicit SPI interface selected.
- **MCP23S17(uint8_t select, uint8_t address = 0x00, SPIClass\* spi = &SPI)** constructor HW SPI with optional address pins and SPI interface.
- **bool begin()** returns true if successful.
- **bool isConnected()** returns true if connected, false otherwise. (dummy for compatibility reasons)
- **uint8_t getAddress()** returns the address set in the constructor. 
Default = 0, range = 0..7.

The two constructors allow to call 4 different constructors.

```cpp
- MCP23S17(10);            // select pin only
- MCP23S17(10, 7);         // select pin + address pins
- MCP23S17(10, 7, &SPI2);  // select pin + address pins + SPI port
- MCP23S17(10, &SPI2);     // select pin + SPI port
```


#### sharing select lines

(not tested)
Technically two chips could use the same select pin and a different address. 
The constructors would allow to setup such a configuration.
I assume that this is less used and IMHO not recommended.


### Single pin interface

- **bool pinMode(uint8_t pin, uint8_t mode)** pin = 0..15, mode = INPUT, OUTPUT. Returns true if successful.
- **bool digitalWrite(uint8_t pin, uint8_t value)** pin = 0..15, value = LOW(0) HIGH (!0). Returns true if successful.
- **uint8_t digitalRead(uint8_t pin)** pin = 0..15, returns LOW or HIGH, might set the lastError();
- **bool setPolarity(uint8_t pin, bool reversed)** pin = 0..15, set reversed flag. Returns true if successful.
- **bool getPolarity(uint8_t pin, bool &reversed)** pin = 0..15, reads reversed flag. Returns true if successful.
- **bool setPullup(uint8_t pin, bool pullup)** pin = 0..15, set pull-up flag. Returns true if successful.
- **bool getPullup(uint8_t pin, bool &pullup)** pin = 0..15, reads pull-up flag. Returns true if successful.


### 8 pins interface

- **bool pinMode8(uint8_t port, uint8_t value)** port = 0..1, value = 0..255. Returns true if successful.
- **bool write8(uint8_t port, uint8_t value)** port = 0..1, value = 0..255. Returns true if successful.
- **uint8_t read8(uint8_t port)** port = 0..1, reads 8 pins into one byte.
- **bool setPolarity8(uint8_t port, uint8_t mask)** port = 0..1, sets polarity for 8 channels at once.
Returns true if successful.
- **bool getPolarity8(uint8_t port, uint8_t &mask)** port = 0..1, reads polarity of 8 channels at once.
Returns true if successful.
- **bool setPullup8(uint8_t port, uint8_t mask)** port = 0..1, sets pull-up for 8 channels at once.
Returns true if successful.
- **bool getPullup8(uint8_t port, uint8_t &mask)** port = 0..1, reads pull-up for 8 channels at once.
Returns true if successful.


### 16 pins interface

- **bool pinMode16(uint16_t value)** value = 0..0xFFFF, returns true if successful.
Returns true if successful.
- **bool write16(uint16_t value)** value = 0..0xFFFF, returns true if successful.
Returns true if successful.
- **uint16_t read16()** reads 16 pins into an uint16_t.
- **bool setPolarity16(uint16_t mask)** sets polarity for 16 channels.
Returns true if successful.
- **bool getPolarity16(uint16_t &mask)** reads polarity of 16 channels.
Returns true if successful.
- **bool setPullup16(uint16_t mask)** sets pull-up for 16 channels.
Returns true if successful.
- **bool getPullup16(uint16_t &mask)** reads pull-up for 16 channels.
Returns true if successful.


###  IO Control Register

Since 0.2.3 the library supports setting bit fields in the IO control register.
Read the datasheet carefully!

- **void enableControlRegister(uint8_t mask)**
- **void disableControlRegister(uint8_t mask)**


|  constant              |  mask  |  description  |
|:-----------------------|:------:|:--------------|
|  MCP23S17_IOCR_BANK    |  0x80  | Controls how the registers are addressed.
|  MCP23S17_IOCR_MIRROR  |  0x40  | INT Pins Mirror bit.
|  MCP23S17_IOCR_SEQOP   |  0x20  | Sequential Operation mode bit.
|  MCP23S17_IOCR_DISSLW  |  0x10  | Slew Rate control bit for SDA output.
|  MCP23S17_IOCR_HAEN    |  0x08  | Hardware Address Enable bit (MCP23S17 only).
|  MCP23S17_IOCR_ODR     |  0x04  | Configures the INT pin as an open-drain output.
|  MCP23S17_IOCR_INTPOL  |  0x02  | This bit sets the polarity of the INT output pin.
|  MCP23S17_IOCR_NI      |  0x01  | Not implemented. 

### Error codes

If one of the above functions return false, there might be an error.

- **int lastError()** Above functions set an error flag that can be read with this function.  
Reading it will reset the flag to **MCP23S17_OK**.

| NAME                    | VALUE  | DESCRIPTION |
|:------------------------|:------:|:------------|
| MCP23S17_OK             |  0x00  | No error    |
| MCP23S17_PIN_ERROR      |  0x81  |
| MCP23S17_I2C_ERROR      |  0x82  | (compatibility)
| MCP23S17_VALUE_ERROR    |  0x83  |
| MCP23S17_PORT_ERROR     |  0x84  |
| MCP23S17_REGISTER_ERROR |  0xFF  | low level.


## Operation

See examples.


## Future

#### must

- improve documentation
  - references to I2C version?

#### should

- keep functional in sync with MCP23017_RT

#### could 

- check need for writing in all functions (Polarity / pullup)
  - check if bit mask changes.
  - what is performance gain vs footprint?
- implement ESP32 specific support in begin()
  - see MCP_ADC.begin()
  - SW_SPI is roughly equal in performance as HW SPI on ESP32.
- investigate and reimplement the INPUT_PULLUP for pinMode() ?

#### wont

- check address range in constructor.