Arduino Driver for Microchip MCP23S17
MCP23S17 Class for Arduino
Introduction:
This class is written to simplify using the Microchip MCP23S17 general purpose I/O expander IC in the Arduino environment. Some understanding of the MCP23S17 is required, so if you are not familiar with it, download the datasheet for it and have a look. The rest of this description will assume a basic understanding of the chip.
Implementation:
The goal of this implementation is to provide a software interface that mimics the existing Arduino I/O functions:
- pinMode(pin, mode)
- digitalWrite(pin, value)
- digitalRead(pin)
The class does include several more methods that can be used to simplify configuration in the same "Arduino-ish" way, methods for writing/reading 8-bit registers (configuration and I/O ports) at once, as well as writing/reading consecutive registers (allowing all 16 bits to be read or written with one method call). The interrupt features of the chip are not directly supported with method for specifically configuring them, however, the byte and word read/write methods may be used to configure and use the interrupt features. These features can get somewhat complicated, and any user prepared to use them will likely prefer the more generic methods for controlling them.
Upon initialization of an MCP23S17 as an object, ALL MCP23S17s on the SPI bus (sharing the same slave select) will be placed into hardware addressing mode. This allows up to 8 MCP23S17s to be used with a single slave select.
Methods:
MCP()
Description
Instantiate an MCP23S17 device as an object.
Syntax
MCP object_name(address, slave_select)
Parameters
object_name: any arbitrary name given to create the object
address: address (0-7) of the device configured with address (pins A0, A1, A2)
slave_select: a valid *Arduino* pin number.
Returns
none
Example
MCP onechip(1, 10); // create an object at address 1 called "onechip", using pin 10 as slave select
MCP twochip(2, 10); // create an object at address 2 called "twochip", using pin 10 as slave select
pinMode()
Description
Configure pin(s) as either input or output on the selected object (device specified by an address)
Syntax
object.name.pinMode(pin, mode);
or
object.name.pinMode(mode);
Parameters
object_name: the name given when this object was created
pin: the pin number (1-16) on which to set as input or output
mode: if a pin is specified, either a "HIGH" (1) for input (default) or a "LOW" (0) for output. If a pin is not specified, mode should be a word indicating the mode of each of the 16 I/O pins on the chip.
Returns
none
Example
void setup() {
onechip.pinMode(4, HIGH); // sets pin 4 as an input
onechip.pinMode(16, LOW); // sets pin 16 as an output
twochip.pinMode(0B0000111100001111); // sets pins 1-4 and 9-12 as input, 5-8 and 13-16 as output
}
pullupMode()
Description
Configure the weak pull-up resistors on pins defined as inputs
This has no effect on pins that are configured as outputs.
Syntax
object_name.pullupMode(pin, mode);
or
object_name.pullupMode(mode);
Parameters
object_name: the name given when this object was created
pin: the pin number (1-16) on which to enable or disable the internal weak pull-up resistor
mode: if a pin is specified, either "HIGH" (1) to enable or "LOW" (0) to disable (default) the weak pull-up resistor on the specified pin. If a pin is not specified, mode should be a word indicating the pull-up mode of each of the 16 pins on the chip. Configuring pull-up has no effect on pins while they are configured as output.
Returns
none
Example
void setup() {
onechip.pullupMode(4, HIGH); // enable the pull-up on pin 4
twochip.pullupMode(0B0000111100000000); // enable the pull-ups on pins 9-12
}
inputInvert()
Description
Configure inversion on pins configured as inputs.
This will cause an inverted input pin to read as "LOW" (0) when it is actually in a high state, or as "HIGH" (1) when it is actually in a low state. This has no effect on pins that are configured as outputs.
Syntax
object_name.inputInvert(pin, inversion);
or
object_name.inputInvert(inversion);
Parameters
object_name: the name given when this object was created
pin: the pin number (1-16) on which to set or clear inversion
inversion: if a pin is specified, either "HIGH" (1) is specified to enable, or "LOW" (0) to disable (default) inversion on the specified pin. If a pin is not specified, mode should be a word indicating the inversion state of each of the 16 pins on the chip. Configuring inversion has no effect on pins while they are configured as output.
Returns
none
Example
void setup() {
onechip.inputInvert(4, LOW); // disable inversion on pin 4
twochip.inputInvert(0B0000000000001111); // enable inversion on pins 1-4
}
digitalWrite()
Description
Write a "HIGH" or "LOW" value to a digital I/O pin(s)
Syntax
object_name.digitalWrite(pin, value);
or
object_name.digitalWrite(value);
Parameters
object_name: the name given when this object was created
pin: the pin number (1-16) who's value will be set
value: if a pin is specified, either a "HIGH" (1) or a "LOW" (0) value may be set on the specified pin. If a pin is not specified, value should be a word indicating the output state of all 16 pins on the device. Writing pins configured as inputs has no effect.
Returns
none
Example
void loop() {
onechip.digitalWrite(16, HIGH); // set pin 16 to "HIGH"
twochip.digitalWrite(0B1100000000110000); // Set 5, 6, 15 & 16 to high, 7,8, 13 & 14 to low - inputs ignored
}
digitalRead()
Description
Reads the value of input pin(s), either "HIGH" ("1") or "LOW" ("0)
Syntax
object_name.digitalRead(pin);
or
object_name.digitalRead();
Parameters
object_name: the name given when this object was created
pin: the pin number (1-16) who's value will be read. If no pin number is supplied, a word will be read containing the input state of all pins. The values for pins configured as output should be disregarded if the "word-mode" version is used.
Returns
"HIGH" (1) or "LOW" (0) if a pin is supplied. a word (16 bits) is returned if no pin argument is given
Example
void loop() {
int onevalue;
int twovalue;
onevalue = onechip.digitalRead(4); // assigns the value of pin4 to onevalue
twovalue = twochip.digitalRead(); // assigns the value of all 16 I/O pins to twovalue
}
wordWrite()
Description:
This is an advanced method to write a register pair in the MCP23S17. This class operates the MCP23S17 in "BANK=0" mode. The intention is that a registers for both ports may be written by supplying a single word as an argument. The low byte is written to the register address supplied, and the high byte to the next higher register address.
Syntax"
object_name.wordWrite(base register, value);
Parameters:
object_name: the name given when this object was created
base register: the beginning register address to write, for example, if 0x02 is given, the low byte of "value" will be written to 0x02 and the high byte of "value" to the register at 0x03
value: a word (unsigned int) that will be broken into two bytes and written to two consecutive registers, starting with the "base register" address
Returns:
none
Example
void loop() {
onechip.wordWrite(0x12, 0xFF00); // Set GPIOA to 0x00 and GPIOB to OxFF
}
byteWrite()
Description:
This is an advanced method to write any single register in the MCP23S17.
Syntax:
object_name.byteWrite(register, value);
Parameters:
object_name: the name given when this object was created
register: the register address to write
value: a byte (unsigned char) that will be written to the specified registers
Returns:
none
Example:
void loop() {
twochip.byteWrite(0x13, 0xF0); // Set GPIOB (portB) to 0xF0 (0B11110000)
}
byteRead()
Description:
This is an advanced method to read any single register in the MCP23S17.
Syntax:
object_name.byteRead(register);
Parameters:
object_name: the name given when this object was created
register: the register address to be read
Returns:
unsigned char (uint8_t)
Example:
void loop() {
int twovalue;
twovalue = twochip.byteRead(0x12); // Read GPIOA (portA)
}
Full Example:
MCP onechip(1, 10); // create an object at address 1 called "onechip", using pin 10 as slave select
MCP twochip(2, 10); // create an object at address 2 called "twochip", using pin 10 as slave select
void setup() {
onechip.pinMode(4, HIGH); // sets pin 4 as an input
onechip.pinMode(16, LOW); // sets pin 16 as an output
twochip.pinMode(0B0000111100001111); // sets pins 1-4 and 9-12 as input, 5-8 and 13-16 as output
onechip.pullupMode(4, HIGH); // enable the pull-up on pin 4
twochip.pullupMode(0B0000111100000000); // enable the pull-ups on pins 9-1
onechip.inputInvert(4, LOW); // disable inversion on pin 4
twochip.inputInvert(0B0000000000001111); // enable inversion on pins 1-4
}
void loop() {
int onevalue;
int twovalue;
onechip.digitalWrite(16, HIGH); // set pin 16 to "HIGH"
twochip.digitalWrite(0B1100000000110000); // Set 5, 6, 15 & 16 to high, 7,8, 13 & 14 to low - inputs ignored
onevalue = onechip.digitalRead(4); // assigns the value of pin4 to onevalue
twovalue = twochip.digitalRead(); // assigns the value of all 16 I/O pins to twovalue
/* These are for context only - use them only if you really know what you're doing
onechip.wordWrite(0x12, 0xFF00); // Set GPIOA to 0x00 and GPIOB to OxFF
twochip.byteWrite(0x13, 0xF0); // Set GPIOB (portB) to 0xF0 (0B11110000)
twovalue = twochip.byteRead(0x12); // Read GPIOA (portA)
*/
}