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Guest
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| 16 bit pointer write problem |
 Posted: Tue Oct 10, 2006 9:47 am |
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Hello,
Just trying to write a 16 bit value from a called function via a pointer. I have defined *=16 to use 16 bit pointers. It appears that only the lower 8 bits are being written when using the following code. The upper byte is left unchanged in program memory. What do i need to do to write the full 16 bits??
Thank you!
| Code: |
#include <16F877>
#device *=16
#fuses HS,NOWDT,NOPROTECT,NOLVP,NOBROWNOUT,NOPUT,NOPROTECT,NOWRT,NOCPD
#use delay(clock=20000000)
void point_back_long(a,b,c,d){
delay_cycles(1);
*a=4;
*b=65535;
*c=65535;
*d=65535;
}
void main(){
int16 a=3,b=256+3,c=512+3,d=1024+3,e=65535;
delay_ms(50);
#ifdef use_lcd
lcd_init();
#endif
//printf(lcd_putc,"\fa before: %lu",a);
delay_cycles(1);
point_back_long(&a,&b,&c,&d,&e);
delay_cycles(1);
//printf(lcd_putc,"\na after: %lu",a);
}
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Guest
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| Posted: Tue Oct 10, 2006 10:33 am |
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To simplify the question, Can i write a 16 bit value value using a pointer? If so how?
Thanks |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Tue Oct 10, 2006 12:01 pm |
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I'm surprised your code compiles without error (but the CCS compiler is known not to be very strict).
I didn't test the result, but at least you should fix the following:
Change | Code: | | void point_back_long(a,b,c,d){ |
to | Code: | | void point_back_long(int16 *a, *b, *c, *d){ |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Oct 10, 2006 12:12 pm |
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All of the parameters have to be declared as int16* (not just the 1st one).
Example:
| Code: |
#include <16F877.h>
#fuses XT, NOWDT, NOPROTECT, PUT, BROWNOUT, NOLVP
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
void point_back_long(int16 *a, int16 *b, int16 *c, int16 *d)
{
*a = 4;
*b = 0xFFFF;
*c = 0xFFFF;
*d = 0xFFFF;
}
//=========================
void main()
{
int16 a = 3;
int16 b = 0x103;
int16 c = 0x203;
int16 d = 0x403;
printf("Before:\n\r");
printf("a = %LX\n\r", a);
printf("b = %LX\n\r", b);
printf("c = %LX\n\r", c);
printf("d = %LX\n\r", d);
printf("\n\r");
point_back_long(&a,&b,&c,&d);
printf("After:\n\r");
printf("a = %LX\n\r", a);
printf("b = %LX\n\r", b);
printf("c = %LX\n\r", c);
printf("d = %LX\n\r", d);
while(1);
} |
The output of the program is:
| Quote: |
Before:
a = 0003
b = 0103
c = 0203
d = 0403
After:
a = 0004
b = FFFF
c = FFFF
d = FFFF |
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Guest
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| Posted: Tue Oct 10, 2006 12:21 pm |
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| Thank you very much for the feedback and the time in running the program. That did the trick. As always you rock, PCM! |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Tue Oct 10, 2006 1:20 pm |
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| PCM programmer wrote: | | All of the parameters have to be declared as int16* (not just the 1st one). |
You are right PCM. I've been programming to long in Delphi and was confused by classic C where we wrote | Code: | | void point_back_long(a, b, c, d) int16 *a, *b, *c, *d; |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Oct 10, 2006 11:00 pm |
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Hi ckielstra,
I wasn't trying to upstage you. I had spent a few minutes
making that test program when I noticed that you had already
replied. I felt like since I put in so much time on it, I might
as well post it. |
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