- FirstAp
- RegAddr
- Status
- Arith
- MidGoto
- LowGoto
- CondJump
- VarMani
- VarArray
- StackOps
- FirstCal
- StakCall
- CallBUp
- Table0
- ArbTable
- SmallTbl
- StateMC
- LEDOn
- Current Consumption Check
- Debounce
- PinChg
- TimeEnd
- Decouple
- WDT
- PowerUp
- Reset
- TMR0
- Random
- Sleep
- DiffOsc
- EEPROM
- SHORT
- ADCLess
- ADC
- VLadder
- PWMOut
- Cylon
- TMR0Int
- LEDPWM
- IntDeb
- TrueRS
- BasicRS
- SimpRS
- 3RS
- Debug
Useful Code Snippets and Macros
"FirstCal" Experiment
The simplest method of passing data to a subroutine is through a register. In the PICmicro, this can be done by either passing a byte parameter between the calling code and the subroutine using the "w" register or using a temporary file register common to both the caller and the routine. Passing data to a subroutine using “w” is always safe, but care has to be taken for returning parameters if “w” is to be used.
The source code listed below can be accessed from the CD-ROM by clicking Here.
title "FirstCal - Passing Subroutine Parms via Registers"
;
; This Program shows how to Pass Parameters back and forth between the
; Mainline and Routines using Registers.
;
; 99.11.13 - Updated for Second Edition
;
; Myke Predko
; 96.05.10
;
LIST P=16F84, F=INHX8M, R=DEC
INCLUDE "p16f84.inc"
; Registers
i equ 12 ; Registers to Operate on
j equ 13
Temp equ 14
__CONFIG _CP_OFF & _WDT_OFF & _RC_OSC
PAGE
; Mainline of FirstCal
org 0
movlw 3 ; Initialized the Variables
movwf i
movlw 5
movwf j
; j = increment( i )
; Pass Parameters using the "w" Register
movf i, w ; Get value to Increment
call increment_w ; Increment using the 'w' Register
movwf j
; Pass Parameters using Temporary Registers
movf i, w ; Get the Value to Increment
movwf Temp
call increment_Temp ; Increment the Temp Value
movf Temp, w ; Store the Incremented Value
movwf j
Finished ; Finished, Just Loop Around Forever
goto $
; Increment Subroutines
increment_w ; Increment the value in "w"
addlw 1 ; Add one to Value in "w"
return
increment_Temp ; Increment the Temporary Value
movlw 1
addwf Temp, f
return
end
FirstCal was modified into FirstC54.asm to demonstrate that the "return" statement can be used with the MPLAB IDE assembler and not get a failure. Repeat the simulation experiment with FirstC54 to see the "retlw 0" instruction replacing the "retun" statement. Depending on the version of the MPLAB IDE you are working with the assembly may return a warning - but an error is never returned. This is one of the reasons why I always make sure my applications assemble "cleanly".
title "FirstC54 - Passing Subroutine Parms via Registers"
;
; This Program is the same as "FirstCal" except the device
; has been changed from a mid-range to a low-end.
;
; 99.11.13 - Created
;
; Myke Predko
;
LIST P=16C54, F=INHX8M, R=DEC
INCLUDE "p16c5x.inc"
; Registers
i equ 12 ; Registers to Operate on
j equ 13
Temp equ 14
__CONFIG _CP_OFF & _WDT_OFF & _RC_OSC
PAGE
; Mainline of FirstCal
org 0
movlw 3 ; Initialized the Variables
movwf i
movlw 5
movwf j
; j = increment( i )
; Pass Parameters using the "w" Register
movf i, w ; Get value to Increment
call increment_w ; Increment using the 'w' Register
movwf j
; Pass Parameters using Temporary Registers
movf i, w ; Get the Value to Increment
movwf Temp
call increment_Temp ; Increment the Temp Value
movf Temp, w ; Store the Incremented Value
movwf j
Finished ; Finished, Just Loop Around Forever
goto $
; Increment Subroutines
increment_w ; Increment the value in "w"
movwf Temp ; - Save in "Temp" for Update
movlw 1 ; Add one to Value in "w"
addwf Temp, w
return
increment_Temp ; Increment the Temporary Value
movlw 1
addwf Temp, f
return
end