Flip Flop Help

izulustudios · 2011-04-01 19:33

Hello and thank you all for this fantastic resource!
I am fumbling around with I suspect is an overly unwieldy amount of code for my application.
My application is as follows:
A set of 8 momentary buttons with an accompanying set of 8 LED's (namely they are illuminated momentary pushbuttons)
I need for each of them to latch; that is, for the corresponding output pin to go high and remain high until any other button is depressed, and for the latch to then shift to the next (random) button to be depressed.
Put very simply: There are 8 buttons, which when pressed, light up and stay lit up until a subsequent button is pressed.
This circuit would be used to control an adjacent system with it's own set of digital inputs and would serve purely as indicator of the last button to have been pressed.
I currently have a convoluted set of IFs, THENs and UNTILs in a big loop, however I suspect there must be a far more elegant way of monitoring a set of 8 dig inputs in one routine and latching a corresponding set of dig outs in another?

Any further guidance would be hugely appreciated.
Thanks again.

Dan

davejames · 2011-04-01 19:43

Hello Dan,

People are gonna ask - would you post your code, please? There may be some things to be done there.

Also (my own curiosity), are you sold on using a Stamp for this rather than some latches?

Regards,

DJ

vaclav_sal · 2011-04-01 19:44

How about simply reset all outputs each time button is press and then set / latch the selected pin?
Vaclav

izulustudios · 2011-04-01 21:08

davejames wrote: »

Hello Dan,
Also (my own curiosity), are you sold on using a Stamp for this rather than some latches?
DJ

Thanks. Yes, my existing version uses 74LS logic latches, however I am hoping to reduce my component list and use a micro.
This will also allow us to change the conditions later, if needed.
Thanks anyway.

izulustudios · 2011-04-01 21:11

vaclav_sal wrote: »

How about simply reset all outputs each time button is press and then set / latch the selected pin?
Vaclav

Thanks Vaclav, that sounds like a great idea.
What is the simplest code definition of "set / latch"?.
Thanks again.

Zoot · 2011-04-01 22:00

This is example presumes all 8 buttons are on 8 adjacent pins and 8 leds on 8 adjacent pins. If not, you could still "map" your inputs to bits in the variables and likewise outputs... this also handles some simple debouncing

leds VAR OUTL
buttons VAR INH

buttonsNow VAR Byte
buttonsLast VAR Byte
idx VAR Nib ' reusable work variable
tmp VAR Byte ' resusable work variable

Start:

OUTS =%0000000000000000  ' all off
DIRS = %0000000011111111 ' pins 0-7 outputs (leds), pins 8-15 inputs (buttons)

PAUSE 100 ' let settle

buttonsNow = buttons ' capture 8 button inputs to byte
buttonsLast = buttonsNow ' seed as "last"

Main:
  ' debounce buttons and capture if different....
  tmp = buttons   ' capture buttons to seed comparison
  FOR i = 0 TO 5  ' should be good for average debounce
      IF buttons <> tmp THEN EXIT   ' if the current state of pins doesn't match, quit the loop
  NEXT
  IF i >= 5 THEN   ' you are only here if the buttons remained stable...
      buttonsNow = tmp   ' move it to "now"
  ENDIF
     
  IF buttonsNow <> buttonsLast THEN ' you had a change from the last time
     leds = buttonsNow  ' move to leds
  ENDIF

 ' the nice thing is you can do other stuff here if you need to, and the leds will be fine and 
 ' you won't miss human button presses... e.g. 

  SEROUT x,y,z, [ tmp ] ' comm with some other device
  SERIN x,y,z, [ tmp ] ' comm with some other device
  
  ' do some other stuff
   


    buttonsLast = buttonsNow  ' save as last -- do it last so you can "parse" state changes if you want...

  GOTO Main

Another nice thing about this setup is it lets you see if a button was "released" or "pressed", e.g.

IF buttonsNow.BIT4 = 1 AND buttonsLast.BIT4 = 0 THEN ' if button 4 is high and it was low, it was pressed...
   DEBUG "button 4 pressed!", CR
ELSEIF buttonsNow.BIT4 = 0 AND buttonsLast.BIT4 = 1 THEN
   DEBUG "button 4 released", CR
ELSEIF buttonsNow.BIT4 = 1 AND buttonsLast.BIT4 = 1 THEN
   DEBUG "let go of it already!", CR
ENDIF

' or...

FOR idx = 0 TO 7
   IF buttonsNow.BIT0(idx) = 1 AND buttonsLast.BIT0(idx) = 0 THEN
      DEBUG "button ", DEC1 idx," pressed!", CR
   ELSEIF buttonsNow.BIT0(idx) = 0 AND buttonsLast.BIT0(idx) = 1 THEN
      DEBUG "button ", DEC1 idx," released!", CR
   ENDIF
NEXT

So.... combining the two to latch only a "press"...

leds VAR OUTL
buttons VAR INH

buttonsNow VAR Byte
buttonsLast VAR Byte
idx VAR Nib ' reusable work variable
tmp VAR Byte ' reusable work variable

Start:

OUTS =%0000000000000000  ' all off
DIRS = %0000000011111111 ' pins 0-7 outputs (leds), pins 8-15 inputs (buttons)

PAUSE 100 ' let settle

buttonsNow = buttons ' capture 8 button inputs to byte
buttonsLast = buttonsNow ' seed as "last"

Main:
  ' debounce buttons and capture if different....
  tmp = buttons   ' capture buttons to seed comparison
  FOR i = 0 TO 5  ' should be good for average debounce
      IF buttons <> tmp THEN EXIT   ' if the current state of pins doesn't match, quit the loop
  NEXT
  IF i >= 5 THEN   ' you are only here if the buttons remained stable...
      buttonsNow = tmp   ' move it to "now"
  ENDIF
     
  IF buttonsNow <> buttonsLast THEN ' you had a change from the last time, check for a press
	FOR idx = 0 TO 7
	   IF buttonsNow.BIT0(idx) = 1 AND buttonsLast.BIT0(idx) = 0 THEN
               leds = buttonsNow  ' move to leds
               EXIT
           ENDIF
        NEXT

  ENDIF

 ' the nice thing is you can do other stuff here if you need to, and the leds will be fine and 
 ' you won't miss human button presses... e.g. 

  SEROUT x,y,z, [ tmp ] ' comm with some other device
  SERIN x,y,z, [ tmp ] ' comm with some other device
  
  ' do some other stuff
  
    buttonsLast = buttonsNow  ' save as last -- do it last so you can "parse" state changes if you want...

  GOTO Main

izulustudios · 2011-04-02 15:44

Wow Zoot, thats awesome, thanks!
I imagined a solution exactly like yours, but was still very hazy with storing the button states as Byte's and the use of OUTS and DIRS.
This really helps me join the dots, so thanks again.

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