Port Variables act like Constants

[MOUNTAIN747]

My project has both USB and RS485 com ports. I would like to switch between active com ports by using a hardware dip switch. This would save a lot of code and time.

   DS1       VAR PortA.1   ;dip switch 
   TX_USB    VAR PortC.6
   TX_RS485  VAR PortC.5
   ComVar    VAR BYTE
    If  DS1=1 then
	ComVar=TX_USB
	Else
	ComVar=TX_RS485
    EndIF
    Serout1 ComVar, 84 [“Transmitting “]

OK, so we know this will not work. Melanie explained why in this post http://www.picbasic.co.uk/forum/showthread.php?t=11801 but stopped short of a solution to the problem, if there is one. I’ve found several posts on this subject, none of which find solutions.
So how do I set a Port Variable within a Serout statement to switch between two ports?

    If DS1=1 then
	ComVar=6
	Else
	ComVar=5
    EndIF
    If ComVar=7 then
	Serout2 PortC.0[ComVar], 84, [“  Com is USB”]
	Else
	Serout2 PortC.0[ComVar], 84, [“  Com is RS485”]
    EndIF

This compiles but it doesn’t work either, Is it for the same reasons the first example failed? There must be some way to solve this problem ??? There must be a different approach that I just haven’t found. Comments please.

[master_olan]

Hi MOUNTAIN747.. why not just use GOTO statements? I think it's easier to do...

        DS1       VAR PortA.1   ;dip switch 
                 
        start:  
         If  DS1=1 then
	   goto tx_usb
         Else
	  goto tx_rs485
         EndIF

        tx_usb:
          Serout portc.6, 84 ["Transmitting USB"]
          goto start
   
        tx_rs485:
          Serout2 portc.5, 84 ["Transmitting RS485"]
          goto start

Adding PAUSE's can help...

[MOUNTAIN747]

Thank you for your reply Olan,
The program has to print out 12 or more different messages when it uploads 30 days of stored data. I’ve run out of EEprom so the messages are at a high cost in code space. If I can use only one message for both USB, which is the primary port, and RS485, which is used only occasionally, it will save 1800 words of code space.

[Darrel Taylor]

Look in the .bas file for the chip you are using.
If it's a 16F877A then open c:\pbp\16f877a.bas

The PORTL and PORTH aliases are used for the PIN numbers (0-15)
PORTL is 0-7 and PORTH is 8-15.

PORTL   VAR     PORTB
PORTH   VAR     PORTC
TRISL   VAR     TRISB
TRISH   VAR     TRISC

If PORTH is aliased to PORTC then you don't need to do anything.
If it's not, change it to PORTC, and change TRISH to alias TRISC.

Then you can use the PIN numbers to access the pins with a variable.

    If DS1=1 then
	ComVar=14   ; PORTC.6
	Else
	ComVar=13   ; PORTC.5
    EndIF

    Serout2 ComVar, 84, [“  Com is PIN - ”, DEC ComVar,13,10]

[MOUNTAIN747]

Darrel,
Thanks again, you make it look so easy! After two days of working with this I now know I was searching for the wrong topics. I haven’t found anything about the .bas file in the manual. I think this subject deserves a WiKi along side your other documents.

By the way, to those who had a hand in creating the Wiki and those who maintain it, ITS GREAT!