The sb-components serial expansion Hat comes with some documentation showing how to add the 2 new UART devices to your Raspberry Pi, however there's nothing to cover how to access the 8 GPIO pins available on this Hat.
I searched github, gitlab, npmjs etc and didn't find any examples of how to access these new ports. So I turned to the datasheet to see if I could work out how to use it.
I've created a nodejs class which exposes some methods to allow access to the GPIO. This chip has a register (0x0B) which is mapped to a single byte, reading this register gives the values of the individual pins. Another register (0x0A) is mapped to a byte which indicates if the pins are inputs or outputs.
Consider the GPIO pins are numbered 0 to 7 which corresponds to bits 0 to 7, some of you will think that's obvious, some will have a lightbulb moment.
Clone the class and copy it into your application. The class depends on the "i2c-bus" module so you'll need to add this to your project if you haven't already:
npm i i2c-bus
Within your application:
const SC16IS752 = require('SC16IS752')
const gpio = new SC16IS752({ i2cAddress: 0x48 })
The i2cAddress is optional and defaults to 0x48 but these Hat's can be modified to use different addresses so the option is there to set it to your own requirements.
- setIn()
- setAllIn()
- setOut()
- setAllOut()
- getBit()
- setBit()
- unsetBit()
- writeByte()
- readByte()
Set a GPIO pin to be an input. All pins default to input.
Example - Set gpio5 to be an input:
gpio.setIn(5)
Set all GPIO pins to be inputs. All ports default to input.
Example - Set all gpio pins to input:
gpio.setAllIn()
Set a GPIO pin to be an output. All ports default to input so you will need to do this if you're defining outputs.
Example - Set gpio3 to be an output:
gpio.setOut(3)
Set all GPIO pins to be outputs. All ports default to input.
Example - Set all gpio pins to be outputs:
gpio.setAllOut()
Get the state of a particular gpio pin.
Example - get the value of gpio6:
const gpio6 = gpio.getBit(6)
Set an output pin to 1 or "on"
Example - set gpio2 on:
gpio.setBit(2)
Set an output pin to 0 or "off"
Example - set gpio2 off:
gpio.unsetBit(2)
Set all the bits in one go. If you know your way around 8-bit binary it's easier to set all the bits in one write.
Given that 1 is on and 0 is off
gpio gpio
7654 3210
|||| ||||
1001 1100 = 0x9C = 156
Writing 156 to the gpio register will set the on's and off's in the pattern seen above.
gpio.writeByte(156)
or
gpio.writeByte(0x9C)
Be aware that only pins set to output will write a value.
1001 1100 <- value to write = 9C = 156
0001 0100 <- inputs and outputs (1 is output, 0 is input)
0001 0100 <- actual value written = 0x14 = 20