Post by thread:[PIC]: Timer Module

Sid Weaver wrote: > I understand it is possible to write a program using Timer 0 or Timer > 1 that runs in the background and generates a square wave. I need a > square wave at 100 Hz 50% duty cycle to pulse large LCDs. > > Can some one tell me how to do this using PBasic, since I don't know > Assembly. I have the F870, F873, F876 and F877. Note: [PIC]: tag added to subject. Sounds like an excellent job for the on-chip PWM module which uses Timer 1. Although it produces ASM code, have a look at the absolutely brilliant "PWM calculator" program thant Tony Nixon posted here just last week. At the very least it will give you a good understanding on how the PWM module works. Tony Nixon wrote: > I just posted a PIC PWM calculator for Windows if anyones interested. > > Set the PWM how you want it and the code is copied to the clipboard > ready for pasting into your ASM file. > > http://www.bubblesoftonline.com/demo/picpwm.zip -- Brent Brown, Electronic Design Solutions 16 English Street, Hamilton, New Zealand Ph/fax: +64 7 849 0069 Mobile/txt: 025 334 069 eMail: spam_OUTbrent.brownTakeThisOuTclear.net.nz -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Yes I agree. When I first thought about it I could see there was a problem with placing the code in the right place. However a look through the manual reveals that you can insert it in a file PBH.INC in the INC subdirectory. I quote " The interrupt handler itself may be placed in the file PBH.INC in the INC subdirectory. Near the end of the file is the label Start. This is where the PICmicro MCU will start executing code on reset, location 0. A few lines down is a section of code that has been commented out. If this code is uncommented, it will enable you to insert your interrupt handler at location 4. Place your assembly language interrupt handler routine after the ORG 4. The routine should end with an RETI instruction to return from the interrupt and allow the processor to pick up where it left off in your PicBasic program." The one last problem is forcing the WSAVE etc variables into the correct bank to make them available where ever the interrupt gets you. It should be possible but I have not found it yet. Still with that in mind you can then use something like this:- PS This is just the interrupt code not the Basic required to initialise TMR1 to start running interrupt etc. Tim MOVWF WSAVE ; SAVE THE W REG SWAPF STATUS,W ; SAVE THE STATUS REG CLRF STATUS MOVWF SSAVE MOVF PCLATH,W ; SAVE THE PCLATH REG MOVWF PSAVE TMR1_VAL =((65536)-(OSC*1250))+7 ; CALCULATE OSC OFFSET VALUES FOR 200HZ INTERRUPTS (OSC = FREQ IN MHZ) BCF T1CON,TMR1ON ; TURN OFF TIMER MOVLW LOW(TMR1_VAL) ADDWF TMR1L,F ; RELOAD TIMER WITH CORRECT VALUE BTFSC STATUS,C INCF TMR1H,F MOVLW HIGH(TMR1_VAL) ADDWF TMR1H,F BSF T1CON,TMR1ON ; TURN IT BACK ON BTFSS PORTX,X GOTO SETBIT BSC PORTX,X ; TOGGLE PORT,X BIT X GOTO EXIT SETBIT BSF PORTX,X EXIT BCF PIR1,0 ; CLEAR TMR1 INTERRUPT FLAG MOVF PSAVE,W ; RESTORE THE PCLATH REG MOVWF PCLATH SWAPF SSAVE,W ; RESTORE THE STATUS REG MOVWF STATUS SWAPF WSAVE,F SWAPF WSAVE,W ; RESTORE W REG RETFIE ; EXIT THE INTERRUPT ROUTIN {Original Message removed}

> Note: [PIC]: tag added to subject. Sounds like an excellent job for > the on-chip PWM module which uses Timer 1. Actually, it uses timer 2. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> > Note: [PIC]: tag added to subject. Sounds like an excellent job for > > the on-chip PWM module which uses Timer 1. > > Actually, it uses timer 2. > Doh! -- Brent Brown, Electronic Design Solutions 16 English Street, Hamilton, New Zealand Ph/fax: +64 7 849 0069 Mobile/txt: 025 334 069 eMail: .....brent.brownKILLspam@spam@clear.net.nz -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics