View source for BoostC Forum Extracts 2007

== In line Assembly ==

http://forum.sourceboost.com/index.php?showtopic=3141&pid=11809&mode=threaded&start=#entry11809


 have a PIC18 device and I'd like to get the address of one of my C variables so I can use a pointer to it in inline assembly. I see in the manual that I can use "movlw _variable" to get the address in the W register, but to set the indirection registers I need 12 bits (8 for FSR0L, and 4 for FSR0H). "movlw _variable" just seems to me to get the lower 8 bits, how do I get the upper bits so I can set up the indirection registers properly?


     #include <system.h>
     int x;

     void main()
     {
      int* xAddr = &x;
     asm
     {
             MOVF _xAddr,W
      
             MOVF _xAddr + 1, W
      }
 }


Using a simple underscore with the c variable name gives you access to the variable in asm
for almost all compilers.


     int x = 2;
     
     asm MOVF _x,W


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http://forum.sourceboost.com/index.php?showtopic=3143&pid=11808&mode=threaded&start=#entry11808

Q:  I have been using the rs232_driver with a pic16f628 on a couple of projects. My question is about including the #define MODE (USART_reset_wdt | USART_HW).

Is it a good idea to setup a wdt when using rs232? I had always just selected the USART_HW and let it go at that. But there have been a couple of times when my boxes would fail to respond and have to be rebooted. I have no idea what the problem was, as it only happened once or twice over months of use.


A:  I think you can enable the watch dog timer. The #define MODE (USART_reset_wdt | USART_HW) will automatically clear your wdt before it resets. I think you might be facing some other problem & not related to wdt. See if your Rx buffers are overflowing and so receive disabled.

Actually you may want to check your pic frequency and the WDT timeout, if they are too close  any extra small delay may randomly hose you if your frequency is not callibrated well.  Remember even crystals have a +/- tolerance percentage and fluctuate with ambient temperature if they are not oven enclosed or compensated.