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electronx
Joined: 07 Aug 2021
Posts: 1
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| rotate_right( ),rotate_left() port shifting -confused |
 Posted: Fri Aug 13, 2021 12:31 am |
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[img] https://ibb.co/Dk24qxh [/img]
| Code: |
#include <16f877a.h>
#fuses XT,NOWDT,NOPUT,NOBROWNOUT,NOLVP,NOCPD,NOWRT,NODEBUG,NOPROTECT
#use delay(clock=4MHz)
void main()
{
int i;
int portb_out;
while(TRUE)
{
portb_out=0b00000001;
for(i=0;i<=7;++i)
{
shift_left(portb_out,??????);
output_b(portb_out);
delay_ms(100);
}
}
}
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Hi everyone , I want to shift the leds, here I want to do it with rotate_left() command. However, even though I read the ccs manual, I could not get out of it.Any help?
Last edited by electronx on Fri Aug 13, 2021 3:48 am; edited 3 times in total |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Aug 13, 2021 2:16 am |
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The output of the program below is as follows:
| Code: |
1 2 4 8 16 32 64 128
1 2 4 8 16 32 64 128
1 2 4 8 16 32 64 128
1 2 4 8 16 32 64 128
1 2 4 8 16 32 64 128
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This was tested in MPLAB vs. 8.92 simulator with CCS vs. 5.104.
| Code: | #include <16F877A.h>
#use delay(crystal=4M)
#use rs232(UART1, baud=9600, ERRORS)
//=================================
void main()
{
int8 i;
int8 portb_out;
while(TRUE)
{
portb_out = 1;
for(i=0;i<=7;++i)
{
output_b(portb_out);
printf("%u ", portb_out);
shift_left(&portb_out, 1, 0);
delay_ms(100);
}
printf("\r");
}
}
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Ttelmah
Joined: 11 Mar 2010
Posts: 19219
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| Posted: Fri Aug 13, 2021 6:23 am |
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It is also worth pointing out that you can just use:
portb_out<<=1;
The point about the rotate_left/shift_left functions, is they are designed
to allow you to do rotations on large numbers of bytes in an array.
So, they require the memory address of the array (&), how many bytes
are to be rotated, and a bit to be shifted 'in' to the start.
Hence how PCM shows.
However C has a built in shift, for a variable, using <<.
The syntax I show is equivalent to:
portb_out = portb_out<<1;
So portb_out is loaded with the value from portb_out shifted left one
bit. The version I show, is the 'shortcut' version of this.
In fact the compiler is smart, and realises it is only dealing with one byte,
so in fact the <<= version, and the shift_left version both result in exactly
the same code. So it comes down to 'taste' on whether you want to use
the CCS function, or the standard C way of doing it. |
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