There are certain chunks of program which perform a general task, which can be useful for all sorts of programs. A large number of these can be found in PIC : Your Personal Introductory Course, however I have compiled a short list of useful bits and pieces here. If you have any suggestions for this sections, don't hesitate to email me with the program segment and an explanation of its function and capabilities.
1. Clearing a long list of file registers :
The FSR should be initialised to the first register to be cleared. STARTReg is the first register of the continuous block that is to be cleared and ENDReg is the file register after the last file register to be cleared. (You can simply replace StartReg and ENDReg in the program segment with the corresponding file registers addresses - or rename them with other used file register names).
movlw STARTReg movwf FSR clrloop clrf INDF ; clears the selected file register incf FSR, f ; moves on to next file register movlw ENDReg ; has it got to the last file reg. ? subwf FSR, w ; ? btfss STATUS, Z ; ? b clrloop ; no, so loops back up.
2. Creating an approximate one second delay using a clock frequency of 4MHz.
(By the way, movf FileReg,w is the same as movwf FileReg)
(Also, the TMR0 has been prescaled by 256 using the OPTION register).
movlw d'16' ; sets up postscaler movwf Post16 ; _1SecDelay movf TMR0, w ; is number in TMR0, 0? btfss STATUS, Z ; ? goto _1SecDelay ; no, so keeps looping incf TMR0, f ; avoides multiple zero read of TMR0 decfsz Post16, f ; has this happened 16 times? goto _1SecDelay ; no, so keeps looping
3. Creating an exact one second delay using a clock frequency of 2.4576MHz.
(The TMR0 has been prescaled by 256 using the OPTION register).
movlw d'80' ; sets up marker to 80 more than addwf TMR0, w ; the current value in TMR0 movwf Mark80 ; movlw d'30 ; sets up postscaler movwf Post30 ; _1SecDelay movf Mark80, w ; has TMR0 reached marker? subwf TMR0, w ; ? btfss STATUS, Z ; ? goto _1SecDelay ; no, so keeps looping movlw d'80' ; updates marker addwf Mark80, f decfsz Post30 ; has this happened 30 times? goto _1SecDelay ; no, so keeps looping