l.s., For delay purposes I need NOP's in an assembler macro, the code below doesn't do the trick. Thread 2267.htm doesn't help me either. A C macroloop, with e.g. DELAY(a); a = 10, slows the execution down too much. Can Anyone help me? thanks, *** #define DELAY(a) \ { \ volatile unsigned b; \ for(b = 0; b < a; b++) \ { \ } \ } #define DELAYNOP \ { \ #pragma asm \ NOP \ NOP \ NOP \ NOP \ NOP \ NOP \ NOP \ #pragma endasm \ }
1) Use a = 9? 2) In <intrins.h> there is an _nop_() function. 3) The following generates a tight loop (an DJNZ instruction )
register unsigned char i; i = count; do { --i; } while( i != 0 );
Hi Bob & Jon, Thanks. I will use the _nop_() for slowing down things. The best way for me is putting as much _nop_()'s in a C macro as I need. This results in about 500nS/_nop_() delay which is, when used 8 times, just enough for me to get it the way I want. When I used the do/while loop one decrement was as much as 14uS and not appropriate. baai, ***.
If you like, you can use assembly code to give you more control on timing issue.
Delay100u: push DPL push DPH mov DPTR, #(65535-10) sjmp DelayLoop Delay50u: push DPL push DPH mov DPTR, #(65535-5) sjmp DelayLoop Delay20u: push DPL push DPH mov DPTR, #(65535-2) DelayLoop: ;About 10uS for 12MHz nop nop inc DPTR mov a, DPH orl a, DPL jnz DelayLoop pop DPH pop DPL ret
"If you like, you can use assembly code to give you more control on timing issue." If you want it to work, you MUST use assembly code - because 'C' gives you absolutely NO control on timing issues! "You can use #pragma asm/endasm to embed to your C code." Better to write a specific assembler function, in an assembler source file. (by all means, use ASM/ENDASM to create the outline of your function - but then throw the 'C' away and just keep it in assembler).