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improve pin.hold() explanation (#428)

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* improve pin.hold() explanation

processed comments by Peter
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gijsio
2021-06-25 10:33:06 +02:00
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content/firmwareapi/pycom/machine/pin.md
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@@ -105,9 +105,31 @@ Get or set the pin pull. Pull can be:
### pin.hold([hold])
Get or set the pin hold. You can apply a hold to a pin by passing `True` (or clear it by passing `False`). When a pin is held, its value cannot be changed by using `Pin.value()` or `Pin.toggle()` until the hold is released. This Can be used to retain the pin state through a core reset and system reset triggered by watchdog time-out or Deep-sleep events. Only pins in the RTC power domain can retain their value through deep sleep or reset.
Get or set the pin hold. This functionality can be used to hold a pin's state after [deepsleep](#machinedeepsleeptime_ms), `machine.reset()` or a [watchdog timer reset](/firmwareapi/pycom/machine/wdt/). Passing `True` will hold the current value of the pin, `False` will release the hold state. When a pin is in hold state, its value cannot be changed by using `Pin.value()` or `Pin.toggle()`, until the hold is released. Only pins in the RTC power domain can retain their value through deep sleep or reset. These are: `P2, P3, P4, P6, P8, P9, P10, P13, P14, P15, P16, P17, P18, P19, P20, P21, P22, P23`
You can use the following example:
```python
from machine import Pin
import machine
p3 = Pin('P3', mode=Pin.OUT)
p3.value(1) #can also be p3.value(0)
p3.hold(True) #hold the pin high
machine.reset()
# instead, you can use:
# machine.deepsleep(10000)
# P3 will still be high here
```
A few things to keep in mind when using the pin hold functionality:
* This feature only preserves the pin value:
* During a (deep)sleep
* After waking up from deepsleep
* After `machine.reset()`
* After a WDT reset
* The hold state itself is not preserved _in Micropython_ after the above mentioned resets. This means that `pin.hold()` will return `False` after such reset, even though the pin is actually still held _in hardware_.
* `pin.hold()` does **not** return the pin's value. You can hold a pin high or low.
* Applying a hard-reset, by for example pressing the reset button, will reset the pin value and release the hold.
These are: `P2, P3, P4, P6, P8, P9, P10, P13, P14, P15, P16, P17, P18, P19, P20, P21, P22, P23`
### pin.callback(trigger, [handler=None, arg=None])