interrupt handling faster than if's?

[keithdoxey]

How are the PICs connected together ? by a wire or by radio/IR link

Do you really need the PRE and SYNCH values to be sent ?

If there is only ever going to be the actual values sent between the PICs then just send the actual values and constantly loop the receiver program like this

Main:
hserin 20,Main [Msg]

Select Case Msg
   Case "1"
          high PORTA.0
   Case "2"
          low PORTA.0
   Case "3"
          high PORTA.1
   Case "4"
          low PORTA.1
   Case "5"
          high PORTA.2
   Case "6"
          low PORTA.2
   Case "7"
          high PORTA.3
   Case "8"
          low PORTA.3
end select
goto main

When no data is being received your program will sit at the Hserin command and return to Main every 20mS if nothing is recevied. Because you are constantly waiting for the Msg the reponse will be instant and because you are only sending one character there should be no possibility of overflow unless three messages are sent in very quick succession but even then it should process them fast enough.

You can then reduce the pause in your transmit program to get a very fast response. Currently you have 200*8 mS of pause in the transmit program so it will take a minimum of 1.6 seconds to complete one loop.

You could also speed up the send program by changing

if (PORTA.0 = 0) AND (sone = 0) then
    hserout [Pre,Synch,"1"]
    sone = 1
    pause 200
endif
if (PORTA.0 = 1) AND (sone = 1) then
    hserout [Pre,Synch,"2"] 
    sone = 0
    pause 200
endif

to

if (PORTA.0 = sone) then           '  input state has changed
  if  PORTA.0 = 0 then               '  port has gone low
        hserout ["1"]                    '  send the command
        sone = 1                         ' record the state
  else
        hserout ["2"]                    ' port has gone high so send the command
        sone = 0                         ' record the state
  end if
  pause 10                     ' may not even need a pause
endif

That way with no switches being changed you only perform 4 tests each program loop and if a switch has changed you perform an additional test. Can probably be optimised further but brain is not fully functional yet... need more coffee

Out of curiosity, why are you storing values opposite to the current state of the pin ?

Personally I would store the current value and detect when it was different. eg

if (PORTA.0<>sone) then      ' state has changed
       sone = PORTA.0           ' store new state
       { do all the other stuff }
endif

[keithdoxey]

Thinking about this further, and assuming you are only using the pin values to send to the other end then

TRANSMITTER

PORTSTATE var Byte
LASTSTATE var Byte


Main:
     PORTSTATE= PORTA & $0F ' mask Port A to retrieve lower 4 pins
     If PORTSTATE <> LASTSTATE then     ' something has changed
            LASTSTATE = PORTSTATE
            Hserout [PORTSTATE]
     Endif
     Pause 10
     Goto Main

RECEIVER

Main:
      Hserin 20,Main, [PortState]
      PortState = PortState ^ $0F  ' EOR to invert pin states (omit this line if you want normal state)
      PORTA = Portstate   ' Set the pins
      Goto Main

That would save loads of program space provided you did not need individual pin states for any other purpose.

Dont forget the set the TRISA registers to configure pins as Inputs and outputs.

NB: There might be slight errors above as I rarely get it right first time!!!!

[mbw123]

Thanks for the many responses. I am going to eventually hook it up to a radio link so I will probably need the Pre and Synch values. Using your code previously posted, I should be able to just add those variables in, right? Thanks again (I will test the code right now)...

-Mike

[mbw123]

One last thing. Will the code (your most recent post before this one) work when two or more buttons are pressed at the same time? Thank you for the help.

-Mike

[keithdoxey]

One last thing. Will the code (your most recent post before this one) work when two or more buttons are pressed at the same time? Thank you for the help.

-Mike

Hi Mike, multiple keypresses shouldnt be a problem as it takes the value of all switches as a 4 bit binary value eg 0110 and sends that to the distant end where you write 1001 (or 0110 if you dont invert) to the output port.

LASTPORT gets set as 0110 ( or 6 if you prefer) and the next time it looks at the port if the value is any different the new value will be sent and stored.

It doesnt matter whether it has changed to 0100, 0111, 1010 etc because all of them are different to 0110 and the entire port value will be replicated at the distand end with just a single command string.