docs/machine.Signal: Improve style/grammar and add usage example.

crypto-aes
Paul Sokolovsky 6 years ago
parent 37379a2974
commit d5336ba136

@ -4,17 +4,44 @@
class Signal -- control and sense external I/O devices
======================================================
The Signal class is a simple extension of Pin class. Unlike Pin, which
The Signal class is a simple extension of the `Pin` class. Unlike Pin, which
can be only in "absolute" 0 and 1 states, a Signal can be in "asserted"
(on) or "deasserted" (off) states, while being inverted (active-low) or
not. Summing up, it adds logical inversion support to Pin functionality.
not. In other words, it adds logical inversion support to Pin functionality.
While this may seem a simple addition, it is exactly what is needed to
support wide array of simple digital devices in a way portable across
different boards, which is one of the major MicroPython goals. Regardless
whether different users have an active-high or active-low LED, a normally
open or normally closed relay - you can develop single, nicely looking
of whether different users have an active-high or active-low LED, a normally
open or normally closed relay - you can develop a single, nicely looking
application which works with each of them, and capture hardware
configuration differences in few lines on the config file of your app.
configuration differences in few lines in the config file of your app.
Example::
from machine import Pin, Signal
# Suppose you have an active-high LED on pin 0
led1_pin = Pin(0, Pin.OUT)
# ... and active-low LED on pin 1
led2_pin = Pin(1, Pin.OUT)
# Now to light up both of them using Pin class, you'll need to set
# them to different values
led1_pin.value(1)
led2_pin.value(0)
# Signal class allows to abstract away active-high/active-low
# difference
led1 = Signal(led1_pin, invert=False)
led2 = Signal(led2_pin, invert=True)
# Now lighting up them looks the same
led1.value(1)
led2.value(1)
# Even better:
led1.on()
led2.on()
Following is the guide when Signal vs Pin should be used:
@ -33,11 +60,11 @@ architecture of MicroPython: Pin offers the lowest overhead, which may
be important when bit-banging protocols. But Signal adds additional
flexibility on top of Pin, at the cost of minor overhead (much smaller
than if you implemented active-high vs active-low device differences in
Python manually!). Also, Pin is low-level object which needs to be
Python manually!). Also, Pin is a low-level object which needs to be
implemented for each support board, while Signal is a high-level object
which comes for free once Pin is implemented.
If in doubt, give the Signal a try! Once again, it is developed to save
If in doubt, give the Signal a try! Once again, it is offered to save
developers from the need to handle unexciting differences like active-low
vs active-high signals, and allow other users to share and enjoy your
application, instead of being frustrated by the fact that it doesn't

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