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MICHAEL Guest
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what's the advantage of #define set_bit_var(x) bit_set (*(in |
Posted: Tue Apr 03, 2007 2:54 pm |
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Hi,
In previous post, I saw macros:
#define set_bit_var(x) bit_set (*(int8 *)(x >>3), x & 7)
#define clear_bit_var(x) bit_clear (*(int8 *)(x >>3), x & 7)
#define read_bit_var(x) bit_test (*(int8 *)(x >>3), x & 7)
I am not sure the advantages of these macros, when CCS already has built-in functions to bit_set, bit_clear and bit_test.
Can some one please clarify. Thanks |
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PCM programmer
Joined: 06 Sep 2003 Posts: 21708
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Posted: Tue Apr 03, 2007 3:15 pm |
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They accept a CCS-style pin number, in a variable, as the argument.
Example:
Code: |
#include <16F877.H>
#fuses HS, NOWDT, BROWNOUT, PUT, NOLVP
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
#define set_bit_var(x) bit_set (*(int8 *)(x >>3), x & 7)
//==========================
void main()
{
int8 pin;
pin = PIN_B0;
set_bit_var(pin);
while(1);
} |
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michael Guest
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Posted: Tue Apr 03, 2007 3:29 pm |
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Hi PCM Programmer,
I tried to compile some examples and the lst files are different. One is writng to the port and the other to the latach. But both perform the same function. May be just for personal prefereces. Regards.
.................... set_bit_var(pin_a0);
002A: BSF F80.0
.................... output_bit (pin_a0, 1);
002C: BSF F89.0
002E: BCF F92.0
....................
.................... clear_bit_var(pin_b0);
0030: BCF F81.0
.................... output_bit (pin_b0, 0);
0032: BCF F8A.0
0034: BCF F93.0
....................
.................... a = read_bit_var(pin_c0);
0036: BCF 06.0
0038: BTFSC F82.0
003A: BSF 06.0
.................... b = bit_test (*PORTC, 0);
003C: BCF 06.1
003E: BTFSC F82.0
0040: BSF 06.1
.................... |
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PCM programmer
Joined: 06 Sep 2003 Posts: 21708
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Posted: Tue Apr 03, 2007 4:03 pm |
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You're using constants as the arguments. Try it with a variable.
If you have vs. 3.249 or before, and if you plug in a variable as
the argument, you will get this compiler error message:
Quote: | Expression must evaluate to a constant |
With vs. 4 of the compiler, CCS has stated that these functions will
now accept a variable. I compiled a test program with the output_bit()
with vs. 4.031 and it does compile OK. There's no error message.
I didn't test it further than that. |
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michael Guest
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Posted: Tue Apr 03, 2007 4:51 pm |
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Hi PCM Programmer,
I am not sure what do you mean by variable.
In the example you posted, pin = PIN_B0. PIN_B0 is 31752 (int16). when assigned to pin (int8), it becomes hex 08. When you plug it in set_bit_var (pin), it will get devided by 8 and use as an int8 pointer and get the content of it and set the bit.
Regards,
#include <16F877>
#fuses HS, NOWDT, BROWNOUT, PUT, NOLVP
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
#define set_bit_var(x) bit_set (*(int8 *)(x >>3), x & 7)
//==========================
void main()
{
int8 pin;
pin = PIN_B0;
set_bit_var(pin);
while(1);
} |
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PCM programmer
Joined: 06 Sep 2003 Posts: 21708
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Posted: Tue Apr 03, 2007 4:57 pm |
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This is a constant:
Code: | #define PIN_B0 31752 |
This is a variable:
(using an int16 because pin numbers in the 18F series are 16-bit constants).
--------------------------
There is quite a difference between passing a variable and passing
a constant to the function. Here is the generated code for my 16F877
example above, when modifed to show both methods:
Code: | pin = PIN_B0;
set_bit_var(pin); // Pass it a variable
set_bit_var(PIN_B0); // Pass it a constant
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Code: |
.................... set_bit_var(pin);
0018: RRF 21,W
0019: MOVWF 77
001A: RRF 77,F
001B: RRF 77,F
001C: MOVLW 1F
001D: ANDWF 77,F
001E: MOVF 77,W
001F: MOVWF 04
0020: MOVF 21,W
0021: ANDLW 07
0022: MOVWF 22
0023: MOVLW 01
0024: MOVWF 77
0025: MOVF 22,W
0026: MOVWF 78
0027: BTFSC 03.2
0028: GOTO 02D
0029: BCF 03.0
002A: RLF 77,F
002B: DECFSZ 78,F
002C: GOTO 029
002D: MOVF 77,W
002E: IORWF 00,F
....................
....................
.................... set_bit_var(PIN_B0);
002F: BSF 06.0
.................... |
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michael Guest
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Posted: Tue Apr 03, 2007 5:36 pm |
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Hi PCM programmer,
Thanks for the clarifications. I compiled using 18F452 and I got similar list files. It is neat the the same macro can work for both 16F and 18F devices. Still that's a lot of instructions to set a bit.
Regards
.................... set_bit_var(c);
003E: RRCF 08,W
0040: MOVWF 03
0042: RRCF 07,W
0044: MOVWF 02
0046: RRCF 03,F
0048: RRCF 02,F
004A: RRCF 03,F
004C: RRCF 02,F
004E: MOVLW 1F
0050: ANDWF 03,F
0052: MOVFF 02,FE9
0056: MOVFF 03,FEA
005A: MOVF 07,W
005C: ANDLW 07
005E: MOVWF 0D
0060: CLRF 0E
0062: MOVLW 01
0064: MOVWF 00
0066: MOVF 0D,W
0068: MOVWF 01
006A: BZ 0074
006C: BCF FD8.0
006E: RLCF 00,F
0070: DECFSZ 01,F
0072: BRA 006C
0074: MOVF 00,W
0076: IORWF FEF,F |
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