not logged in | [Login]
Setting a pin to a digital value
import pyb g = pyb.Pin(pin_id, mode, pull) # mode and pull are optional arguments and default to input and no-pullup # e.g. if: # X1 is how the pin is labeled on the board, # using X1 for output to control an LED, # we want a pullup resistor on the output. g = pyb.Pin('X1', pyb.Pin.OUT_PP, Pin.PULL_UP) g.low() # sets the pin low g.value(True) # sets it high, g.value(False) # sets it lowReading a digital value from a Pin
g = pyb.Pin('X1', pyb.Pin.IN) state = g.value() # no argument to value means read.
There are several ways to identify the pin to control:
mypin = pyb.Pin.board.X1
mypin = pyb.Pin.cpu.C12
pyb.Pin.dict["LeftMotorDir"] = pyb.Pin.cpu.C12
mypin = pyb.Pin("LeftMotorDir")
and use it like so:
g = pyb.Pin(mypin, pyb.Pin.OUT_PP) or
g = pyb.Pin(mypin, pyb.Pin.OUT_PP, Pin.PULL_UP)
A pin can act in one of the following modes:
Pin.IN- configure the pin for input
Pin.OUT_PP- configure the pin for output, with push-pull control
Pin.OUT_OD- configure the pin for output, with open-drain control
Pin.AF_PP- configure the pin for alternate function, pull-pull
Pin.AF_OD- configure the pin for alternate function, open-drain
Pin.ANALOG- configure the pin for analog input. You may prefer to use pyb.ADC instead.
You would use push-pull control to actively drive the output high or low (use it as a current source or current sink). For example, if you connect an LED (using a resistor) between GND and the pin, the LED will light up if you drive the pin high. Since you configured the output to be push-pull, it will act as a current source here. Otherwise, if you switch an output to open-drain, it will only act as a current sink (it will drive low if you write 0 to it), but it can not deliver high level output if you switch it to its "1" state. This configuration could be used together with I2C devices, where an external pull-up resistor on SCL and SDA ensures high level and all bus nodes can only drive these bus lines to low level.
The Altenate function settings are used when the specific chipset has allocated a pin to do several functions internally, e. g. use the pin as SPI, UART, I2C, timer output etc. This alternate function is turned on by setting an internal register. This setting defines how thepPin mode will be handled if this is alternate function is active.
A pin can have the following pull-up settings:
Pin.PULL_NONE- no pull up or down resistors - This is the default
Pin.PULL_UP- enable the pull-up resistor
Pin.PULL_DOWN- enable the pull-down resistor
We can use the pin directly or use the ADC. The ADC gives you more control.
Reading an analog value from a pin directly:
g = pyb.Pin('X1', pyb.Pin.ANALOG) state = g.value() # no argument to value means read.For more details on using the ADC see here.
Pins also have the ability to trigger an interrupt and do an action when the digital value of the pin changes. To do this we use Pin.ExtInt
import pyb key_interrupt = pyb.ExtInt(pin_id, pyb.ExtInt.IRQ_FALLING, pyb.Pin.PULL_UP, callback) #E.g. if: # - You want to call the function count() when # - the pin X1 is pulled low then key_interrupt = pyb.ExtInt('X1', pyb.ExtInt.IRQ_FALLING, pyb.Pin.PULL_UP, count)Note:
Valid modes are:
IRQ modes are used for ... EVT modes allow ...
Other useful functions for external interrupts are:
extint.disable()Disable the interrupt associated with the ExtInt object. This could be useful for debouncing.
extint.enable()Enable a disabled interrupt.
extint.line()Return the line number that the pin is mapped to.
extint.swint()Trigger the callback from software.
Last edited by Thoralt Franz, 2014-05-07 05:59:01