MCP23S17

Arduino library for MCP23S17 16 channel SPI port expander.

Description

This 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.

The write1(pin, value) is optimized. If a pin is not changed it will not be written again to save time.

0.5.0 Breaking change

Version 0.5.0 introduced a breaking change to improve handling the SPI dependency. The user has to call SPI.begin() or equivalent before calling MCP.begin(). Optionally the user can provide parameters to the SPI.begin(...)

0.4.0 Breaking change

The version 0.4.0 has breaking changes in the interface. The rationale is that the programming environment of the Arduino ESP32 S3 board uses a remapping by means of the include file io_pin_remap.h. This file remaps the pins of several core Arduino functions. The remapping is implemented by #define macros and these implement "hard" text replacements without considering context. The effect is that methods from this class (and several others) which have the same name as those Arduino core functions will be remapped into something not working.

The following library functions have been renamed:

old name	new name	notes
analogRead()	read()
analogWrite()	write()
pinMode()	pinMode1()
digitalRead()	read1()
digitalWrite()	write1()

0.3.0 Breaking change

The version 0.3.0 has breaking changes in the interface. The essence is removal of ESP32 specific code from the library. This makes it possible to support the ESP32-S3 and other processors in the future. Also it makes the library a bit simpler to maintain.

Related

16 bit port expanders

• https://github.com/RobTillaart/MCP23017_RT
• https://github.com/RobTillaart/MCP23S17
• https://github.com/RobTillaart/PCF8575
• https://github.com/RobTillaart/TCA9555

8 bit port expanders

• https://github.com/RobTillaart/MCP23008
• https://github.com/RobTillaart/MCP23S08
• https://github.com/RobTillaart/PCF8574

Interface

#include "MCP23S17.h"

Constructor

• MCP23S17(uint8_t select, uint8_t dataIn, uint8_t dataOut, uint8_t clock, uint8_t address = 0x00) constructor SOFTWARE SPI.
• MCP23S17(int select, SPIClassRP2040* spi) constructor HARDWARE SPI with explicit SPI interface selected.
• MCP23S17(int select, SPIClass* spi) constructor HARDWARE SPI with explicit SPI interface selected.
• MCP23S17(int select, int address = 0x00, SPIClassRP2040* spi = &SPI) constructor HARDWARE SPI with optional address pins and SPI interface.
• MCP23S17(int select, int address = 0x00, SPIClass* spi = &SPI) constructor HARDWARE SPI with optional address pins and SPI interface.
• bool begin(bool pullup = true) initializes library, returns true if successful. Default sets the pins to INPUT PULLUP. Returns false if not connected or a register could not be set.
• 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 hardware constructors allow to call 4 different constructors.

- 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

(verified in #19)
Technically two chips could use the same SELECT pin and a different address. Since 0.2.5 the constructors allow to setup such a configuration. The added value is that one can use up to 8 devices (= 128 IO lines) with only four lines (MISO, MOSI, CLOCK, SELECT).

I assume that this configuration is less used and IMHO not recommended. NB it is more difficult to detect which device is selected when debugging.

To use the hardware addresses the Hardware Address ENable register must be set. See datasheet 3.3.2 ADDRESSING SPI DEVICES, need to set IOCON.HAEN.

The library supports two ways:

MCP.enableControlRegister(MCP23S17_IOCR_HAEN);  //  or 0x08
or
MCP.enableHardwareAddress();  //  0.2.5 version and up

See also IO Control Register section below.

Single pin interface

• bool pinMode1(uint8_t pin, uint8_t mode) pin = 0..15, mode = INPUT, OUTPUT. Returns true if successful.
• bool write1(uint8_t pin, uint8_t value) pin = 0..15, value = LOW(0) HIGH (!0). Returns true if successful.
• uint8_t read1(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.
• bool write16(uint16_t value) value = 0..0xFFFF, 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.

The reading and writing to registers have been performance optimized for the 16 bit interface. If there are problems please open an issue.

Interrupts (experimental 0.5.2)

Read the datasheet for the details, page 24,25.
Note: Error handling is limited.

pin = 0..15
mode = { RISING, FALLING, CHANGE }

• bool enableInterrupt(uint8_t pin, uint8_t mode) Returns true if successful. Returns MCP23S17_PIN_ERROR if pin > 15.
• bool disableInterrupt(uint8_t pin) Returns true if successful. Returns MCP23S17_PIN_ERROR if pin > 15.

16 pin interface, overrides all earlier settings. Sets all pins to the same interrupt mode { RISING, FALLING, CHANGE }.

• bool enableInterrupt16(uint16_t mask, uint8_t mode) mask = 0x0000..0xFFFF.
• bool disableInterrupt16(uint16_t mask)

Determine which pins caused the Interrupt. (datasheet).

• uint16_t getInterruptFlagRegister() Reads all 16 pins.

• uint16_t getInterruptCaptureRegister() Reads all 16 pins. Is used to detect if multiple pins triggered an interrupt.

• bool setInterruptPolarity(uint8_t ipol) polarity: 0 = LOW, 1 = HIGH, 2 = NONE/ODR

• uint8_t getInterruptPolarity() return set value.

Merge INTA and INTB into one signal so only one line handles all interrupts. This reduces the number of interrupt lines to handle, however one has to read more registers to find the changed ones.

• bool mirrorInterrupts(bool on) enables / disables mirror mode.
• bool isMirroredInterrupts() returns set option (0,1 or 2).

SPI

• void setSPIspeed(uint32_t speed) set hardware speed (8Mb default).
• uint32_t getSPIspeed() returns set speed.

Debugging

• bool usesHWSPI() returns true = hardware SPI, false = software SPI.
• int lastError() idem.

IO Control Register

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

• bool enableControlRegister(uint8_t mask) set IOCR bit fields
• bool disableControlRegister(uint8_t mask) clear IOCR bit fields

constant	mask	description
MCP23x17_IOCR_BANK	0x80	Controls how the registers are addressed.
MCP23x17_IOCR_MIRROR	0x40	INT Pins Mirror bit.
MCP23x17_IOCR_SEQOP	0x20	Sequential Operation mode bit.
MCP23x17_IOCR_DISSLW	0x10	Slew Rate control bit for SDA output.
MCP23x17_IOCR_HAEN	0x08	Hardware Address Enable bit (MCP23S17 only).
MCP23x17_IOCR_ODR	0x04	Configures the INT pin as an open-drain output.
MCP23x17_IOCR_INTPOL	0x02	This bit sets the polarity of the INT output pin.
MCP23x17_IOCR_NI	0x01	Not implemented.

Two dedicated functions are added: (MCP23S17 only)

• bool enableHardwareAddress() set IOCR_HAEN bit.
• bool disableHardwareAddress() clear IOCR_HAEN bit.

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.
MCP23S17_INVALID_READ	0xFF	low level.

Future

Must

• Improve and extend documentation
• add examples

Should

• keep functional in sync
  • sync error codes to MCP23x17
• buy additional hardware
• test with multiple devices.
  • multi SELECT lines
• add example with interrupts
  • test
  • extend error codes
• optimize code - squeeze footprint
• fix TODO's in code
• IOCON.HAEN, Hardware Address ENable.
  • should this be enabled in begin() by default? 0.3.0
  • check address range in constructor.

Could

• check need for writing in all functions (Polarity / Pull-up)
  • check if bit mask changes.
  • what is performance gain vs footprint?
• investigate and reimplement the INPUT_PULLUP for pinMode() ?
• initial value (16 bit?) as begin parameter (breaking change)
  • depends on input output pull-up etc
• AVR software SPI optimize
  • dao and clock - see fastShiftOut.

Wont

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