Post by thread:[PIC]: 16F877 TMR0 Problem

Hello, I've been playing with PIC for a while now and have created a number of units based on the 16F84 range. Just lately I've migrated to the PIC16F877 and using the ICD have developed a graphical display unit with LCD etc etc. This all works 100% O.K. I'm using HiTECH C. The problem is this..... I've been trying to get the TMR0 timer0 to increment once per instruction cycle on my PIC16F877. This would at first appear very very simple. I have done this before without any problem on the PIC16F84. It also works perfectly under simulation but....... The hardware PIC16F877 appears to randomly increment the TMR0 register as soon as I set TOCS=0 and I cannot see any reason for this. Even single assembler instructions to set the TMR0 register to a value do not work. With TOCS=1 I can set TMR0 to any value I like but of course it doesn't do anything as I don't have any clock source on T0CKI. I have included (In the next email!!!) a sample program below (written for HITECH C). This code functions perfectly under simulation but neither my hardware (20MHz) or the ICD demo board (4Mhz) function properly. I also compiled it for the PIC16F84 and that ran perfectly as well so it only the PIC16F877 that seems to get upset? I would not suspect my hardware as it also does this on the "Advanced Transdata" demo board that came with my ICD. I have also tried to do this under MPLAB movlw 0xA movwf 0x1 but it does not work!!! Unless I have T0CS=1 which is pretty stupid. TMR0 just goes on blindly changing at random. I've checked the register bank select bits are being set to bank0 where TMR0 is located at address 0x1. I am at a complete loss and cannot work out why the same program works fine for the 16F84 but not the 16F877 ???? I hope you can help as this has now crippled my product and I'm going nowhere fast. Thanks Pete spam_OUTpeterTakeThisOuTtrlperformance.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

Here is the sample HiTECH C program I cannot get to work on the PIC16F877 What am I doing wrong? Thanks Pete #include <pic.h> typedef unsigned char UINT8; typedef unsigned short UINT16; #define TIMER_PRESET 50 /*************************************************************************** *** * Subroutines ;*************************************************************************** ***/ /*----------------------------- initalisation --------------------------------*/ void init_pic(void) { // Configure TMR0 Port and interrupts TRISC = 0x0; T0CS = 0; // Timer increments on instruction clock T0IE = 1; // Enable interrupt on TMR0 overflow INTEDG = 1; // Rising edge trigger the interrupt INTE = 1; // enable the external interrupt RB0 change GIE = 1; // Global interrupt enable } /*************************************************************************** *** * Interrupt Service Routine **************************************************************************** */ static void interrupt isr(void) { /*-------------------------- TMR0 timer interrupt ---------------------------*/ if (T0IF) { TMR0 = TIMER_PRESET; T0IF = 0; // clear the interrupt flag } } /* ****************************** END ISR ************************************/ void main(void) { UINT8 counter=0; UINT16 counter1=0; init_pic(); background_tasks: if ( counter1 == 0) { PORTC = counter; counter++; } counter1++; goto background_tasks; } ///////////////////////////// END OF FILE //////////////////////////////////// -- 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

just a guess but I don't see you assigning the prescaler to the WDT, OPTION register PSA = 1? If not, the prescaler will default to TMR0 with whatever PS0-PS2 are set to, 000 being a 1:2 rate. Bill At 07:39 PM 06/07/2002 +0100, you wrote: {Quote hidden}>Here is the sample HiTECH C program I cannot get to work on the PIC16F877 > >What am I doing wrong? >Thanks >Pete > >#include <pic.h> > >typedef unsigned char UINT8; >typedef unsigned short UINT16; > >#define TIMER_PRESET 50 > >/*************************************************************************** >*** > * Subroutines >;*************************************************************************** >***/ >/*----------------------------- >initalisation --------------------------------*/ >void init_pic(void) > { > // Configure TMR0 Port and interrupts > > TRISC = 0x0; > > T0CS = 0; // Timer increments on instruction clock > T0IE = 1; // Enable interrupt on TMR0 overflow > INTEDG = 1; // Rising edge trigger the interrupt > INTE = 1; // enable the external interrupt RB0 change > GIE = 1; // Global interrupt enable > } > >/*************************************************************************** >*** > * Interrupt Service Routine > >**************************************************************************** >*/ >static void interrupt >isr(void) >{ >/*-------------------------- TMR0 timer >interrupt ---------------------------*/ > if (T0IF) { > TMR0 = TIMER_PRESET; > T0IF = 0; // clear the interrupt flag > > } >} >/* ****************************** END ISR >************************************/ > >void main(void) >{ > UINT8 counter=0; > UINT16 counter1=0; > init_pic(); > >background_tasks: > > if ( counter1 == 0) > { > PORTC = counter; > counter++; > } > counter1++; > > goto background_tasks; >} > >///////////////////////////// END OF FILE >//////////////////////////////////// > >-- >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 > > -- 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

http://www.piclist.com/postbot.asp?id=piclist\2002\06\07\153942a Thanks for the reply and yes I hadn't assigned the Prescaler in that example,BUT this is not the real problem. I have written other code to select the prescaler for the TMR0 but is not that the PIC isn't counting/timing at the correct rate it's more drastic.... *** the TMR0 register is just RANDOMLY changing **** I can see no sequence in the numbers at all. They appear to just change at will on every instruction. When I run this in the simulator all is well and I get the TMR0 register changing as expected. So why NOT on the real hardware??? I have now written it in assembler and still I must be missing something obvious... ; Use PIC16F84 and set radix system to decimal LIST P=16F877, R=DEC ;****************************************************************************** ; Include header file ;****************************************************************************** #include "p16f877.inc" #define TIMER_PRESET 180 ;****************************************************************************** ; equates ;****************************************************************************** ; WORDS status_temp equ 0x0c w_temp equ 0x0d ;****************************************************************************** ; START of CODE ;****************************************************************************** org 0x0 ; reset vector goto init ; jump over subroutines org 0x4 ; Interrupts goto isr ; Goto this service routine ;****************************************************************************** ; initalisation ;****************************************************************************** init clrf PORTC ; set = 0 bsf STATUS,RP0 ; BANK1 movlw 0x00 movwf TRISC movlw b'11011111' ; movwf OPTION_REG ; Set Timer ON and use prescaler of 256 bcf STATUS,RP0 ; Retrun to BANK0 movlw TIMER_PRESET movwf TMR0 ; Reset Timer0 bsf INTCON,T0IE ; Turn Timer Interrupt On bsf INTCON,INTE ; Turn RB0 Change Interrupt On bsf INTCON,GIE ; Turn Global Interrupts On ;****************************************************************************** ; main program ;****************************************************************************** main background_loop goto background_loop ;****************************************************************************** ; Interrupt Service Routines ;****************************************************************************** isr ; --------------------------- save context ------------------------------------ context_save movwf w_temp ; save off W and STATUS registers swapf STATUS, w movwf status_temp clrf STATUS ; select Bank0 ; ************************* TIMER TMR0 Interrupt ****************************** tmr0_int ; ----------------------- Clear Interrupt Condition -------------------------- bcf INTCON,T0IF ; Clear pending interrupt flag ; ------------- Reset TMR0 Timer State for next timed interrupt -------------- movlw TIMER_PRESET movwf TMR0 ; Reset Timer0 tmr0_int_end ; ******************** restore context saved on entry to ISR ******************* isr_end context_restore swapf status_temp, w ; restore all registers movwf STATUS swapf w_temp, f swapf w_temp, w ; -------------------- END of interrupt service routine ----------------------- retfie ; Return from interrupt service routine ;****************************************************************************** ;****************************************************************************** ;****************************************************************************** end ; ------------------------------ END OF FILE ---------------------------------- --- Peter R Betts http://www.piclist.com/member/PRB-TRL-AA7 PIC/PICList FAQ: http://www.piclist.com -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu

Hi Peter. I just did an MPLAB sim on your asm version. It works as you would expect. I also ran it as a 16C73 on my trusty old PICmaster emulator (won't do 877s) and it works the same as the sim. TMR0 increments by ones and twos as advertised depending on the instruction type. BTW, your equates need to be moved up to 0x20 or higher. Right now, they are in the middle of the SFRs. Now for the real question -- is your program really working and your emulator just isn't showing you or is there really something wrong? What you should do is calculate your TMR0 interrupt rate and toggle an output pin. Monitor the pin with a scope to see if it happens at the right rate. If it does, at least you can keep developing with some degree of confidence until we can sort out why TMR0 doesn't look like it works. If not, might be time to call your emulator manufacturer and talk to him. Bill At 08:08 AM 06/10/2002 +0100, you wrote: > http://www.piclist.com/postbot.asp?id=piclist\2002\06\07\153942a > >Thanks for the reply and yes I hadn't assigned the Prescaler in that example,BUT this is not the real problem. > >I have written other code to select the prescaler for the TMR0 but is not that the PIC isn't counting/timing at the correct rate it's more drastic.... > >*** the TMR0 register is just RANDOMLY changing **** >I can see no sequence in the numbers at all. They appear to just change at will on every instruction. > >When I run this in the simulator all is well and I get the TMR0 register changing as expected. >So why NOT on the real hardware??? > >I have now written it in assembler and still I must be missing something obvious... > >; Use PIC16F84 and set radix system to decimal > LIST P=16F877, R=DEC > code snipped... -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestKILLspammitvma.mit.edu

Bill, > I just did an MPLAB sim on your asm version. It works as you > would expect. Great, it worked for both the 16F84 and 16F877 sim' targets and the 16F84 hardware debugger but not the 16f877 (with small changes between the software versions for target compatibility). > equates need to be moved up to 0x20 or higher. Right now, they are in the > middle of the SFRs. Doh! O.K. That was me trying to hack something quick in ASM to prove a point. The Hitech C version should have all that sorted properly. It may be masking something however. > is your program really working and your emulator just isn't showing you or is there really something > wrong? Ummm... I see. Yes I could execute some LED (pin) toggling in the ISR as a test and measure with my scope. That would prove its rate is fixed or random. > until we can sort out why TMR0 doesn't look like it works. This might be the case. The code did call the ISR function but I didn't measure the period between calls, only stopped the debugger and checked the TMR0 register value. It may have just randomly hit 0 and triggered or in fact counted up and wrapped around as required. > If not, might be time to call your emulator manufacturer and talk to him. Its the MicroChip made ICD (In Circuit Debugger) with the latest (last week) downloaded firmware. Thanks for your help Pete -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestspam_OUTTakeThisOuTmitvma.mit.edu

I have seen something like this before, my timer worked fine then suddenly it would go berserk and shoot off into hyperspace, after trying everything we could think of I noticed a hair-line solder bridge between two outputs, so when one turned on it tried to drag the other one up and the PIC didn't like it at all, but crucially didn't totally stop working either. It wasn't visible with the naked eye, and we only saw it when we got the board under a microscope, it's worth considering, we got too stuck on the software and didn't consider a hardware problem could possibly cause an apparent software problem :{ Good luck ! Jonathan Starr R&D Technician Electronix Limited Tel +44 (0)1993 700510 Fax +44 (0)1993 700511 e-mail jonathansspam_OUTelectronix.co.uk web http://www.electronix.co.uk This e-mail has been sent to you by Electronix Ltd. This communication is intended for the addressee only, is private and confidential, and is subject to the applicable terms and conditions. If you are not the intended recipient, any disclosure, copying or distribution of this information is strictly prohibited. -- {Quote hidden}>Hi Peter. >I just did an MPLAB sim on your asm version. It works as you would expect. >I also ran it as a 16C73 on my trusty old PICmaster emulator (won't do >877s) and it works the same as the sim. TMR0 increments by ones and >twos as >advertised depending on the instruction type. BTW, your equates need to >be >moved up to 0x20 or higher. Right now, they are in the middle of the SFRs. > >Now for the real question -- is your program really working and your >emulator just isn't showing you or is there really something wrong? What >you should do is calculate your TMR0 interrupt rate and toggle an output >pin. Monitor the pin with a scope to see if it happens at the right rate. >If it does, at least you can keep developing with some degree of confidence >until we can sort out why TMR0 doesn't look like it works. If not, might >be time to call your emulator manufacturer and talk to him. > >Bill > >At 08:08 AM 06/10/2002 +0100, you wrote: > http://www.piclist.com/postbot.asp?id=piclist\2002\06\07\153942a > >Thanks for the reply and yes I hadn't assigned the Prescaler in that example,BUT this is not the real problem. > >I have written other code to select the prescaler for the TMR0 but is not that the PIC isn't counting/timing at the correct rate it's more drastic.... > >*** the TMR0 register is just RANDOMLY changing **** >I can see no sequence in the numbers at all. They appear to just change at will on every instruction. > >When I run this in the simulator all is well and I get the TMR0 register changing as expected. >So why NOT on the real hardware??? > >I have now written it in assembler and still I must be missing something obvious... > >; Use PIC16F84 and set radix system to decimal > LIST P=16F877, R=DEC > code snipped... -- http://www.piclist.com hint: To leave the PICList @spam@piclist-unsubscribe-requestKILLspammitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList KILLspampiclist-unsubscribe-requestKILLspammitvma.mit.edu

> Are you running this with an ICD? YES. > the timer will increment for every instruction that the ICD code executes as well, not just the destination code. Oh know!!!! Really???? That would explain a heck of a lot. Never even considered that. Sees obvious now you mention it. > I seem to remember a warning about this somewhere in the ICD documentation. Trust me to miss that little gem. I'll try to find this in the ICD doc's. Does the ICD execute extra cycles ONLY when processing a breakpoint or stepping etc, when the debugger has to communicate with the host or does it run a few cycles all the time in the background? (Sorry if this is in the doc's I'm not at home to look them up) I'm trying to get a constant 10ms interrupt that will sample my ADC inputs and then spend the rest of the time processing the data and displaying on an LCD screen (which is slow!) Obviously I do not want this to vary as it's my main sampling rate. Thanks for the reply, I think this is the answer. Pete -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

>Does the ICD execute extra cycles ONLY when processing >a breakpoint or stepping etc, when the debugger has to >communicate with the host or does it run a few cycles >all the time in the background? (Sorry if this is in >the doc's I'm not at home to look them up) This should only be a problem while in the ICD code. Just remember that it is a program in your programming space that has been enabled by a special bit of hardware that has in effect caused a special interrupt. >I'm trying to get a constant 10ms interrupt that will >sample my ADC inputs and then spend the rest of the >time processing the data and displaying on an LCD >screen (which is slow!) Obviously I do not want this >to vary as it's my main sampling rate. Well I would say that to do this you are best to get the operations to a point where they work correctly, i.e. the A/D operation, and the LCD operation, and then dispense with the ICD and have printf(debug message) messages going over a serial interface to a terminal when you let it rip so you are not stopping your code. -- http://www.piclist.com hint: To leave the PICList spamBeGonepiclist-unsubscribe-requestspamBeGonemitvma.mit.edu

> Just remember that it is a program in your programming space that has been enabled > by a special bit of hardware that has in effect caused a special interrupt. Yes, I forgot that. All to easy to think it's a real emulator. > Well I would say that to do this you are best to get the > operations to a > point where they work correctly, i.e. the A/D operation, and the LCD > operation, and then dispense with the ICD Yep. At least now I feel happy about carrying on. Over the weekend I was pulling my hair out. Seems so simple now I know. I know all the seperate bits work if I run everything in a big background task. I just needed to get a constant periodic sampling interval to make the numbers displayed meaningful and went off on a tangent. Thanks for all your help everyone. Pete now with a big smile -- http://www.piclist.com hint: To leave the PICList TakeThisOuTpiclist-unsubscribe-requestEraseMEspam_OUTmitvma.mit.edu

>> *** the TMR0 register is just RANDOMLY changing **** I can see no sequence in the numbers at all. They appear to just change at will on every instruction. When I run this in the simulator all is well and I get the TMR0 register changing as expected. So why NOT on the real hardware??? << How are you "seeing" timer 0 values on the real hardware? With the in circuit debugger I perhaps? I'm not familiar with the in circuit debugger since I use the ICE, but doesn't that thing execute code on the target for each "single step"? If so, that would explain the additional timer 0 increments. Timer 0 behaves very nicely with the ICE. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu