;********************************************************************** ; ; Filename: flashLEDs.asm ; Date: $Date: 2003/03/05 01:33:04 $ ; File Version: $Id: flashLEDs.asm,v 1.1 2003/03/05 01:33:04 jerry Exp $ ; $Source: /home/cvsroot/projectsTop/picProjectBoard/examples/mplab_example/flashLEDs.asm,v $ ; Author: Jerry Dunmire ; ;********************************************************************** ; ; Notes: ; ; This program will flash the 4 discrete LEDs on the ECPE5 PIC ; project board. The pattern will be 0x5, 0xA at 5 Hz rate. ; ; See the ATTENTION and WARNING notes embedded below! ; ;********************************************************************** list p=16f877 ; list directive to define processor #include ; processor specific variable definitions ; '__CONFIG' directive is used to embed configuration data within ; .asm file. The labels following the directive are from the ; p16f877.inc file. ; ; ATTENTION! This config setting is ignored when the file is ; loaded with WLoader. ; ; BUT! XWisp crashes when it attempts to set the config ; register. Apparently WLoader does not return a ; response that XWisp understands. The program is ; successfully loaded, but the 16F877 is still in ; program mode (WLoader running) until you remove ; the serial cable and press the reset button. ; You will have to completely exit XWisp and ; restart. ; ; WARNING! So since this program is intended for use with ; the ECEP5 PIC Project board using WLoader, the ; config setting below is commented out. If you ; try to use this program with another PIC programmer ; you will almost certainly have to un-comment this ; line (unless your programmer allows a manual ; config setting). ; ; WARNING! The config value below is the default value ; from the template file Microchip provided with ; v6.10 of the PIC IDE. I have not checked the ; values to see if they are correct for this ; program. ; __CONFIG _CP_OFF & _WDT_ON & _BODEN_ON & _PWRTE_ON & _RC_OSC & _WRT_ENABLE_ON & _LVP_ON & _DEBUG_OFF & _CPD_OFF ;***** VARIABLE DEFINITIONS w_temp EQU 0x70 ; variable used for context saving status_temp EQU 0x71 ; variable used for context saving ;********************************************************************** ; ; Start vector ; ; ATTENTION! ; For use with WLoader, it is important that the first ; instruction at 0x000 be a goto statement. WLoader will relocate that ; goto statement and use it to start the program. The actual goto ; statement at 0x000 is a jump to the WLoader program. ; ; The template file (f877temp.asm) provided by Microchip starts ; with the 'clrf PCLATH' command (which is commented out below). ; My reading of the 16F877 data sheet indicates the PCLATH register ; is cleared on power-on or software reset,so I'm not sure why ; the template includes the clrf PCLATH command. Anyway, a 'clrf ; PCLATH command is incompatible with WLoader. ; ORG 0x000 ; processor reset vector goto main ; go to beginning of program ;********************************************************************** ; ; Interrupt handler ; ; Simply invert the value in port C and clear the interrupt flag. ; The W register doesn't really need saved for this code, but ; it probably would for most ISRs- so leave the save/restore W ; code in place as starting point for other ISRs ; ORG 0x004 ; interrupt vector location movwf w_temp ; save off current W register contents movf STATUS,w ; move status register into W register movwf status_temp ; save off contents of STATUS register comf PORTC, f bcf PIR1, 0 ; clear the TIMER0 interrupt flag movf status_temp,w ; retrieve copy of STATUS register movwf STATUS ; restore pre-isr STATUS register contents swapf w_temp,f swapf w_temp,w ; restore pre-isr W register contents retfie ; return from interrupt ;********************************************************************** ; Main code section ; ; An initial value is written to the port C (the low 4 bits control the ; LEDs). Then each time Timer 0 overflows an interrupt will be generated. ; The interrupt service routine will inverte the value in port C causing ; LEDs that were on to turn off and visa versa. ; ; By using the largest prescaler setting for Timer 1 (1:8) the period ; between interrupts will be: ; Fosc = 20MHz ; Fosc/4 = 5MHz = prescaler_clock ; prescaler_clock/8 = 625000 Hz = clock ; ; period = 1 / (clock/(2^16)) = 1 / (625000 / 65536) = ~104.9 ms ; main ; Setup port C output lines and set and intial output value bcf STATUS, RP0 bsf STATUS, RP0 ; select bank 1 to get at the TRISC register clrf TRISC bcf STATUS, RP0 ; PORTC and T1CON (below) are in bank 0 movlw 0x05 movwf PORTC ; setup timer 0 movlw B'00110001' ; |||||||+-- 1 = start timer ; ||||||+--- 0 = internal clock (Fosc/4) = 5MHz for our board ; |||||+---- x = ignored for internal clock ; ||||+----- 0 = Timer1 external OSC disabled ; ||++------ 11 = 1:8 Prescaler (clock = 5MHz / 8) ; ++-------- xx = unimplemented movwf T1CON ; Enable Timer1 overflow interrupt bsf STATUS, RP0 ; PIE1 is in bank 1 movlw B'00000001' ; |||||||+-- 1 = Timer1 overflow interrupt enabled (TMR1F) ; ||||||+--- 0 = TMR2 to PR2 match interrupt disabled ; |||||+---- 0 = CCP1 interrupt disabled ; ||||+----- 0 = SSP interrupt disabled ; |||+------ 0 = USART xmit interrupt disabled ; ||+------- 0 = USART recv interrupt disabled ; |+-------- 0 = A/D Converter interrupt disabled ; +--------- 0 = Parallel port r/w interrupt disabled movwf PIE1 bcf STATUS, RP0 ; return to bank 0 to set INTCON ; INTCON setup movlw B'11000000' ; |||||||+-- 0 = Port B change interrupt flag clear ; ||||||+--- 0 = RB0/INT flag clear ; |||||+---- 0 = Timer0 overflow interrupt flag clear ; ||||+----- 0 = Port B change interrupt disabled ; |||+------ 0 = RB0/INT interrupt disabled ; ||+------- 0 = Timer0 overflow interrupt disabled ; |+-------- 1 = Peripheral Interrupts enabled ; +--------- 1 = All (global) interrupts enabled movwf INTCON ; sleep - can't use the sleep command because it ; will turn off the main oscillator that we are using ; for the timer! ; ; Instead we'll just waste time (and power) doing nothing. wait nop goto wait END ; directive 'end of program'