LED ON and OFF with 2 Push button switches

[fratello]

http://ww1.microchip.com/downloads/e...Doc/40040c.pdf
Regards !

[mikejp56]

Hi fratello,
Thanks for the link.
Regards,
mike

[Art]

It’s a flip-flop, so if you do it in software a flip-flop might as well be 1 bit of memory.
You’re going to want to look a the LED in a real program and know if it’s on or off,
so will usually want to store the LED state which would usually represent some program state.

flipflop var bit ‘ 1 = LED is on 0 = LED is off
debounce var byte ‘ button debounce counter
flipflop = 0 ‘ start with LED off at power up, or on if you want to
debounce = 0 ‘ reset debounce counter

trisb.0 = 1’ button pin input
trisb.7 = 0’ LED pin output

cycle: 'program cycle

if debounce > 199 then
if portb.0 = 1 then
flipflop = 1
debounce = 0
else
flipflop = 0
debounce = 0
endif
endif

if flipflop = 1 then ‘ set LED to flip flop state
portb.7 = 1
else
portb.7 = 0
endif

if debounce < 200 then ‘ increment button debounce counter
debounce = debounce + 1
endif

goto cycle ‘ repeat loop forever

[Dave]

But that's only using 1 button Art not 2 as in the title of the thread.....

[Art]

But that's only using 1 button Art not 2 as in the title of the thread.....

Whoops!
No need to accommodate contact bounce for the buttons then.

flipflop var bit ‘ 1 = LED is on 0 = LED is off
flipflop = 0 ‘ start with LED off at power up, or on if you want to

trisb.0 = 1’ buttonA pin input ON
trisb.1 = 1’ buttonB pin input OFF
trisb.7 = 0’ LED pin output

cycle: 'program cycle

if portb.0 = 1 then
flipflop = 1 ‘ set memory bit
endif
if portb.1 = 1 then
flipflop = 0 ‘ reset memory bit
endif

portb.7 = flipflop ‘ set LED on or off

goto cycle ‘ repeat loop forever

[Dave]

Now, Thats nice and easy. The only thing I would change is not having a variable for the state of the output pin but reading the output state.

[Art]

In the long run, for midrange pics that don’t have a port latch register,
we should be using a byte port latch to avoid RWM error if time allows.
So it would go, write single bit to port latch byte, write entire port latch byte to port, read back bit from port latch byte.
Not that I can say I’ve ever encountered a problem I’d put down to RWM error.