Maximum frequency output from a PIC - Page 2


Closed Thread
Page 2 of 2 FirstFirst 12
Results 41 to 69 of 69
  1. #41
    Join Date
    Oct 2012
    Posts
    81


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    As the wise man once said “necessity is the mother of invention”.
    I’m sure that it will take you no time to build a “tool” to solve your problem. What about employing one more PIC to do the job for you? Set it up to count incoming pulses from your DUT for a set period of time and send the results to a LCD or to your preferred PC communication terminal for a visual. You just built yourself a home made, dirty cheap frequency counter ready to solve your problem now and help you in the future.
    Just a thought.
    Some experimenting and results in that matter were done in the beginning of this thread but unless you are starting with a really high clock flexibility is not that great. I’m not sure if the Assembly approach will bring any more advantage but, again it is out of my league.


    Regards,

    Nick

  2. #42
    Join Date
    Aug 2003
    Posts
    985


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Looks like I'll have to.
    I always thought if I have a 5 Volt square wave,
    that my multimeter would measure it as 2.5 Volts.
    I never considered the sampling frequency of the multimeter has
    no connection with the frequency of the signal being measured.

  3. #43
    Join Date
    Oct 2012
    Posts
    81


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Hi again,

    I’m trying to move what I learned last week to a larger PIC (PIC16F819) which I have a lot of leftovers and I’m trying to make use of. I’m also trying to increase my output frequency by using a 16MHz oscillator.

    Based on what the data sheet shows I should have about the same setup as I had with PIC12F683 except that I could select between RB2 and RB3 as my output.

    With the above code I get good output on RB1 (led out which proves that the system is running) but I do not get any output on RB2 or RB3. I was hoping that it will go by default on one of them.
    Code:
    @	device  pic16F819, wdt_off, hs_osc, pwrt_on, mclr_off, lvp_off, protect_on
    DEFINE OSC 16         ' We're running at 16 Mhz
    
    ADCON1=%01001110            ' Digital only for all pins
    
    led     var         PORTB.1
    i       var         byte
    
    CCP1CON = %00001100     ' Normal PWM 
    PR2 = 3            
    CCPR1L =0         
    CCP1CON.5 = 1
    CCP1CON.4 =1
    
    For i = 0 to 9
        Toggle LED
        Pause 500
    NEXT
    
    Main:
        high led
        CCP1CON = %00001100     ' Normal PWM mode
        T2CON.2 = 1             ' Timebase ON
        PAUSE 15
    
        low led
        T2CON.2 = 0             ' Timebase OFF
        CCP1CON = %00000000     ' Disable PWM to regain control of PortA.2
        PAUSE 5
    Goto Main
    The data sheet states:

    The CCP module’s input/output pin (CCP1) can be
    configured as RB2 or RB3. This selection is set in bit 12
    (CCPMX) of the Configuration Word register.

    I have no idea how to change this setting and if this is the reason why I get no output.
    Is there anything that I should do differently?

    Thank you in advance for any input.

    Nick

  4. #44
    Join Date
    Oct 2005
    Location
    Sweden
    Posts
    3,517


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Hi Nick,

    1) Add _CCP1_RB2 or _CCP1_RB3 to your line of config directives in order to select which pin to be used as the CCP1-pin. But yes it WILL default to one of them.

    2) When the PIC starts all pins are set to be input. You need to set RB2 or RB3 to be an output by clearing the coresponding bit in the TRISB register. The reason the LED works is because commands like TOGGLE, HIGH and LOW handles clears the TRIS-bit for you - each and every time the command is executed.....

    3) Not that it matters but anyway, as far as I can see the 16F819 can not do 16MHz on its internal oscillator, up goes the partcount you said you want to keep low. If running at 16MHz is the main reason for switching to the 16F819 you could just as well stuck that 16MHz oscillator on the 12F683.

    /Henrik.

  5. #45
    Join Date
    Oct 2012
    Posts
    81


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Hi Henrik,

    Thank you for pointing out my stupid mistake. I knew it must be something I overlooked.
    In my defense I have to say that after copying the code from 683 I made the necessary changes on the top of the code to apply it to 819. In the process I removed the TRISIO line from the old code and look up the corresponding line for 819. I got distracted (which is quite easy at my age) and did not finish it. My mind was set that I did it so I was looking for something else.

    I will add extra configs and test it again after work tonight.

    To answer your question why I’m using an external oscillator: I would like to experiment with higher frequencies and I have plenty of 819 (some of them on PCBs ready to use as prototyping boards).
    I will order some more oscillators (or try to locate the ones I have somewhere in my garage) for all PBP supported frequencies and have a wide range of available frequencies in the range of 250KHz to 5MHz. Also I could not find any PIC supported by my setup that will do more than 8MHz on internal oscillator.
    After Art’s post I realized that my signal generator outputs only signals lower than 2MHz so I have to compensate for the difference.
    I’m doing the same thing with the 683 (recycling old rev boards) but the 683 version is extremely small (less than 1² inch) and they do not have the padding for the oscillator.
    For the working project I’m still using the low part count concept.

    Regards,

    Nick

  6. #46
    Join Date
    Oct 2012
    Posts
    81


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    I've added the two extra configs and I got output on RB2.
    I did not have time to play more but I will do as soon as I will return from a two weeks vacation.

    Regards,

    Nick

  7. #47
    Join Date
    Aug 2003
    Posts
    985


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    You could try putting the code you want to be called the fastest, closest to zero vector.
    Labels called with a Goto command causes the program counter to start looking for your label from zero,
    so the closest it is to zero, the faster it is found, and run.

    So without looking at anything else about your code:


    Code:
    // the following is not run time code, so who cares…
    @	device  pic16F819, wdt_off, hs_osc, pwrt_on, mclr_off, lvp_off, protect_on
    DEFINE OSC 16         ' We're running at 16 Mhz
    led     var         PORTB.1
    i       var         byte
    
    // jump to config vector
    Goto Config
    
    Main:
        high led
        CCP1CON = %00001100     ' Normal PWM mode
        T2CON.2 = 1             ' Timebase ON
        PAUSE 15
    
        low led
        T2CON.2 = 0             ' Timebase OFF
        CCP1CON = %00000000     ' Disable PWM to regain control of PortA.2
        PAUSE 5
    Goto Main
    
    
    Config:
    ADCON1=%01001110            ' Digital only for all pins
    CCP1CON = %00001100     ' Normal PWM 
    PR2 = 3            
    CCPR1L =0         
    CCP1CON.5 = 1
    CCP1CON.4 =1
    
    For i = 0 to 9
        Toggle LED
        Pause 500
    NEXT
    
    // run main program
    Goto Main

  8. #48
    Join Date
    Oct 2012
    Posts
    81


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    This is a nice tip Art.
    I will only have the chance to try it after my well overdue vacation, just for fun.

    Just so I understand your tip correctly for the sample code presented it will make the GOTO jump in the main loop much faster in which case the main loop will be faster and the second half of the loop will be closer to the target 5 mS?

    For my particular application this is not a big advantage but for time sensitive applications it might make a difference. All I need in this case is to create a 20 mS frame with a 15 / 5 mS ratio.
    I can only guess that the Rx program might benefit from that but in my case the really fast action happens behind the scene and I think that the system is pushed to its maximum.

    I was always under the impression that each PBP command has a fixed amount of execution time but your suggestion proves me wrong.

    How is your project going?

    One correction to my statements few posts ago: I mentioned that I will try to increase my available frequencies by employing a PIC16F819 with higher frequency external oscillators to cover 2 MHz – 5 MHz band but I just realized that my math was wrong. For some reason I was under the impression that you can get a maximum Fosc / 4 out of PWM module but the formula proves me wrong again, it is only Fosc / 8. I think that I was biased by the fact that the Fosc / 4 is available on clock out feature.
    Anyway recycling few boards that will only collect dust in my garage is still good enough even though the expected results are a bit lower.

    Regards,

    Nick

  9. #49
    Join Date
    Aug 2003
    Posts
    985


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Yes, as I understand, the major delay per cycle is the "Goto Main".
    It's not my suggestion that proves you wrong, it's you timing it

    Then if you work out how long the Goto takes to execute, you can
    subtract that from the 5 value in your PAUSE 5 command, and you're
    fine until you put anything between the start of your program and the
    end of main, or also if you use a beefy command like sound, or serin/out
    etc., as they put code in the front of your program for the same reasons
    (they want to execute fast also).

  10. #50
    Join Date
    Oct 2005
    Location
    Sweden
    Posts
    3,517


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Hi,
    I'm definitely no expert on the low level stuff but I do think there's some misunderstaning / confusion going on here.

    When you execute a GOTO Label it's NOT like the program starts from the top and then "searches" thru the code until it finds the Label to which you want to GOTO.

    The physical adress of the piece of code starting "at" Label is known when the program is compiled so the GOTO Label is simply replaced with GOTO $xxxx where xxxx is the physical adress in program memory where the particular piece of code is located. A GOTO always takes TWO instruction cycles, no more no less.

    But, some PICs have its program memory divided into pages and when a GOTO is executed it's important that it GOTO's the adress in the correct page. The compiler handles this for you when needed (that's the warning you see sometimes, Code crosses page boundries or something like that). Making sure you're in the correct page does take a couple of instructions as well so all in all the GOTO CAN take more than 2 instruction cycles but not much. So it CAN make a (small) difference rearanging the routines so it doesn't need to jump across page boundires when executing a GOTO but most of the time you simply wouldn't care.

    In this particular case the GOTO Main will take 2 cycles. Only if the Main routine would end up starting in one page and ending in the next would it take more than 2 cycles.

    Interrupt service routines are one thing where it can matter. Since the hardware interrupt vector is at adress $0004 (IIRC) it makes sense (if you're looking for the absolute best performance) to place your interrupt service routine at the top of the program (and jump over it of course). If you don't do this it MIGHT end up in another memory page and you'll loose a few cycles every time it needs to set the correct page bits before jumping to the ISR.

    Again, I'm no expert so I might very well have some details wrong - I'm happy to be corrected.

    /Henrik.

  11. #51
    Join Date
    Jan 2009
    Location
    Miami, Florida USA
    Posts
    637


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Henrik,

    I don't have the definitive answer either, but I think that what Art is suggesting makes sense to me. I have tried moving to the beginning of the program subroutines that I use a lot in the program and the used programming code space is reduced by a good number of bytes. So, I assume that the program is also executing faster. I believe that this has something to do with the way the program memory is organized in pages in many PICs.

    Robert
    "No one is completely worthless. They can always serve as a bad example."

    Anonymous

  12. #52
    Join Date
    Oct 2005
    Location
    Sweden
    Posts
    3,517


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Hi,
    On the 12F683 and 16F819 there is only one page of program memory so it doesn't (or shouldn't if my reasoning is correct) matter where you put anything because there will never be a need to switch pages.

    If I understand what Art wrote correctly he's basically claiming that the "further" the GOTO jump is, the longer it takes and the further "down the list" your subroutines are placed the longer it takes to GOSUB them because the program counter starts "searching for them" from the beginning of the program. I don't think that is correct - neither on PICs with a single memory page nor on those with multiple pages.

    If using a PIC with the program memory spanning several pages and it has to jump (GOTO or GOSUB) from ona page to another then the compiler will insert code to make sure the correct page is selected before executing the GOTO but it either does that or it doesn't and that piece of code (to select the correct page) will be always take the same amount of time (a couple of cycles I imagine), it doesn't matter where or "how far" it is going to jump.

    /Henrik.

    EDIT: Robert, which PIC did you use in the project where you moved the subroutines?
    Last edited by HenrikOlsson; - 21st September 2013 at 11:56.

  13. #53
    Join Date
    Aug 2003
    Posts
    985


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    That is right sorry, I have my interpreted and compiled BASICs mixed up.

    It's probably not bad practice anyway, so that your fast code is not kicked
    out of the first page when you add picbasic's macro type commands such
    as serin/out, DTMF, SOUND, pauseus, etc.
    It also matters with C later on, to to avoid forward declarations.

    It makes me wonder now, if every goto command also has the PCLATH
    command with it, or if picbasic waits till the program extends past the 2K page (probably does).

    You also turned off the watchdog, but didn't tell PBP not to insert clrwdt commands.
    You would only need a single asm "@ clrwdt" inside the whole Main loop,
    and calculate that into your subtract from the delay time,
    but they are likely in the PAUSE commands, and factored into timing I think.

  14. #54
    Join Date
    Oct 2005
    Location
    Sweden
    Posts
    3,517


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Nope, not bad practice at all, I just don't see it making any difference in this application. But again, do try it - I might be wrong!

    As for tweaking the delay time, it's a good thing to keep in mind for when timing is REALLY criticial but for this application, I don't know.... IMHO it's making things WAY more complicated than it is....

    We're talking 20ms total period time here (ideal), 15ms 'carrier on', 5ms 'carrier off'. The PIC is running at 8MHz so each instruction is 500ns, it takes two instruction cycles to GOTO Main, add another couple of instructions for the rest, lets call it 20 in total - the actual period would be 20.01ms, an error in timing of 0.05%, I think that miniscule error will be swamped by the inacuracy of the internal oscillator. Of course, it MIGHT matter but then you need something better than the internal oscillator to run it.

    /Henrik.

  15. #55
    Join Date
    Jan 2009
    Location
    Miami, Florida USA
    Posts
    637


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Henrik,

    I think used a PIC16F727 when I did that. I think I got that idea of moving the most used subroutines to the beginning of the program when reading a post by Melanie. It had something to do with saving programming space in a PIC. I will try to find that thread later.
    "No one is completely worthless. They can always serve as a bad example."

    Anonymous

  16. #56
    Join Date
    Jan 2009
    Location
    Miami, Florida USA
    Posts
    637


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    "No one is completely worthless. They can always serve as a bad example."

    Anonymous

  17. #57
    Join Date
    Aug 2003
    Posts
    985


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Henrik was right there, I was selling PBP short.
    It shouldn't matter with PBP programs under 2K anyway,
    but you'll appreciate the practice if you use another language.

    You remember the old interpreted BASIC with line numbers?
    Code:
    10 CLRSCREEN
    20 PRINT "HELLO WORLD"
    30 GOTO 20
    It's the goto in that one that searches a list to find the line/label it's after.
    In this case (30 GOTO 20), it searches from the beginning, but if the destination
    line is after the GOTO command, it searches from the GOTO command onward.
    Some interpreted Pic BASIC language (not PBP) probably does the same thing
    even if you don't need to use the line numbers anymore.

    If you just want to check a byte variable is in BANK0 to access it without switching,
    you can increment it with inline assembler.
    Code:
    @ incf _B1;
    should be the same as
    Code:
    B1 = B1 + 1;
    If byte B1 was not in BANK0, a different variable or some unassigned RAM will be incremented.

  18. #58
    Join Date
    Oct 2005
    Location
    Sweden
    Posts
    3,517


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Hi,

    Robert,
    Yes, the 16F727 has its program memory divided into four pages so I can see it making a difference on that one. But still, I'm not cyet onvinced that having them "first" is what actually helps, I believe it's more like where they (the subroutines that is) are relative to where the calls TO them are. I mean, calling subroutines in page 0 from Main in page 1 should be no different from calling subroutines in page 1 from Main in page 0....it needs to switch page in both cases.

    Darrel or anyone - are you listening? Care to share some details?

    Art,
    If that interpreted BASIC, whichever it is, really works like that it kind of sucks - big time IMO.
    As for the rest, you're now talking about RAM and not program memory.

    /Henrik.

  19. #59
    Join Date
    Jan 2009
    Location
    Miami, Florida USA
    Posts
    637


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Yes, unfortunately I don't know the facts either. It would be good if somebody else clarifies this point here.
    "No one is completely worthless. They can always serve as a bad example."

    Anonymous

  20. #60
    Join Date
    Oct 2005
    Location
    Sweden
    Posts
    3,517


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    I've posted a question on the MELABS support forum. Hopefully Darrel or someone else will give us some insight.

    /Henrik.

  21. #61
    Join Date
    Aug 2003
    Posts
    985


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Quote Originally Posted by HenrikOlsson View Post
    Hi,
    Art,
    If that interpreted BASIC, whichever it is, really works like that it kind of sucks - big time IMO.
    As for the rest, you're now talking about RAM and not program memory.

    /Henrik.

    The second part is in relation to the link posted (keeping vars in BANK0 - avoiding switch statements).

    I will try to explain why it is important to put code you want to run fast at the beginning of your PBP program,
    even though I was incorrect as to one of the reasons why, there are more, and PBP actually does this in the
    compiled assembler program (with it's own function calls, not yours) whether you like it or not.

    You want to keep most called functions (PBP routines) in the first 2K code space to avoid page switching.
    You also want to keep most used variables in Bank0 to avoid bank switching (for RAM).

    Say you fill up the first 2K page with code, and run into the second code page,
    then introduce a serin or serout command in the second code page.
    PBP doesn't put the serin command where you wrote it.
    Every PBP macro command such as serial is placed at the beginning of the generated
    assembler code, which kicks some of your your PBP code out of the first 2K code space.
    What is placed where you wrote the serial command is a series of gosubs that pass
    individual bytes to the assembler routine which has been placed at the beginning of the asm source.

    You wil notice that if you use a second serial command, your code size doesn't massively increase again
    because the original asm routine that was inserted by the first serial command is reused.

    When you use a serin, and serout command, this is the decompiled assembler that is placed
    at the beginning of your compiled code to deal with it:
    Code:
    SerialIN							;receive serial byte with pre-determined timeout
      movf		R6		,W				;move timeout delay to temp
      movwf		R0						;
      movf		R15		,W				;
      movwf		R9						;
      movlw		0x01						;
      movwf		R1						;set inside loop counter
      clrf		R10						;
    serial_loop							;
      clrwdt							;keep watchdog timer clear
      call		SerinX						;get one bit
      btfss		status		,C				;wait for start bit
      goto		serinstart					;
      decfsz	R1		,F				;
      goto		serial_loop					;
      movlw		0xFF						;
      addwf		R10		,F				;
      btfsc		status		,C				;
      goto		serial_loop					;
      addwf		R0		,F				;
      btfss		status		,C				;
      addwf		R9		,F				;
      btfss		status		,C				;
      goto		DoneX						;time out
      movlw		0x32						;
      movwf		R1						;reset inside loop counter
      clrw								;
      movwf		R10						;
      goto		serial_loop					;
    SerialIN_notimeout						;
      clrwdt							;receive byte serialy with no timeout
      call		SerinX						;get one bit
      btfsc		status		,C				;wait for start bit
      goto		SerialIN_notimeout				;
    serinstart							;
      call		serialdelay					;wait 1/4 bit time
      clrf		R4						;zero parity accumulator
      movlw		0x08						;number of bits in one byte
      movwf		R10						;
    serpar								;
      call		seroutdelay					;wait bit time
      call		SerinX						;get one bit
      btfsc		status		,C				;accumulate parity
      incf		R4		,F				;
      btfss		R14		,05				;if no parity...
      clrf		R4						;...keep it even
      rrf		R1		,F				;move bit into byte
      decfsz	R10		,F				;check for more bits
      goto		serpar						;
      btfsc		R14		,05				;if parity...
      bcf		R1		,07				;...clear top bit of result
      call		seroutdelay					;delay to stop bit
      bsf		status		,C				;carry shifts in clear
      movf		R1		,W				;get char to W
      return							;
    SerinX								;
      movf		RR2		,W				;receive one bit for serial in
      movwf		fsr						;
      movf		RR1		,W				;
      bsf		fsr		,07				;
      iorwf		indf		,F				;
      bcf		fsr		,07				;
      andwf		indf		,W				;
      btfsc		R14		,06				;
      xorwf		RR1		,W				;
      addlw		0xFF						;
      return							;
    SerialIN_skipbyte						;
      movf		R13		,W				;ignore received byte for serial in
      bsf		status		,C				;
      btfsc		status		,Z				;
      goto		DoneX						;
      call		skipX						;
      btfss		status		,C				;
      return							;
      decf		R13		,F				;
      goto		SerialIN_skipbyte				;
    
    serialOUT							;transmit byte serialy from port pin
      movwf		R3						;save byte to send
      movf		RR2		,W				;get port to fsr
      movwf		fsr						;
      movlw		0x80						;zero parity accumulator (preserve blanking)
      andwf		RM2		,F				;
      movlw		0x08						;1 start bit + 7 data bits
      movwf		R12						;
      bcf		status		,C				;start bit low
    seroutloop							;
      btfsc		status		,C				;accumulate parity bits
      incf		RM2		,F				;
      call		seroutbit					;send a bit and delay bit time
      rrf		R3		,F				;move to next bit
      decfsz	R12		,F				;do next bit, if any
      goto		seroutloop					;
      nop								;
      btfsc		R14		,05				;send parity
      rrf		RM2		,W				;get parity to carry
      call		seroutbit					;send parity or last bit and delay bit time
      call		Done						;
      bsf		status		,C				;stop bit high
      call		seroutbit					;send stop bit and delay bit time
      movf		R16		,W				;do pacing
      movwf		R10						;
      movf		R7		,W 				;
      goto		DelayX						;
    seroutbit							;
      bcf		fsr		,07				;make sure we're pointing to the port
      btfss		R14		,07				;check for TRIS mode
      goto		seroutnorm					;handle normal mode
      movf		indf		,W				;get port data
      iorwf		RR1		,W				;set bit on
      btfss		R14		,06				;bit matches invert mode
      xorwf		RR1		,W				;set bit off
      movwf		indf						;write it out
      bsf		fsr		,07				;point fsr to port tris
      movf		indf		,W				;get tris data
      iorwf		RR1		,W				;make bit an input
      btfss		status		,C				;bit direction matches bit
      xorwf		RR1		,W				;make bit an output
      movwf		indf						;write it out
      goto		seroutdelay					;wait remainder of bit time
    seroutnorm							;
      movf		indf		,W				;get port data
      iorwf		RR1		,W				;set bit on
      btfss		status		,C				;skip if bit should be on
      xorwf		RR1		,W				;set bit off
      btfsc		R14		,06				;invert if 'N' mode
      xorwf		RR1		,W				;flip for invert
      movwf		indf						;write it out
      bsf		fsr		,07				;point fsr to port tris
      comf		RR1		,W				;get complemented bit mask to W
      andwf		indf		,F				;clear tris bit to set output
      goto		seroutdelay					;wait remainder of bit time
    serialdelay							;
      bsf		RM2		,06				;
    seroutdelay							;
      movf		R14		,W				;get high baud byte
      andlw		0x1F						;mask to our bits
      addlw		0xFF						;fix baud
      movwf		R9						;save it
      movf		R5		,W				;get low baud byte
      addlw		0xF5						;
      btfsc		status		,C				;bump up high byte if low overflowed
      incf		R9		,F				;
      btfss		RM2		,06				;
      goto		pauseUSL					;
      bcf		RM2		,06				;clear short delay mark
      movwf		R0						;save low part
      movlw		0x02						;divide time by 4
      call		shiftR						;
      goto		pauseUSL					;do 1/4 delay
    That's quite a lot of code asking to be placed in the first 2K code space (and kicking your code out).
    The serial always appears to be placed first, then SOUND, then EEPROM, then PAUSE.

    If you use any PAUSE command, this is inserted:
    Code:
    Delay
      clrf		R10						;delay 1
    DelayX								;
      movwf		R1						;delay 2
    DelayXX								;
      movlw		0xFF						;
      addwf		R1		,F				;
      btfss		status		,C				;
      addwf		R10		,F				;
      btfss		status		,C				;
      goto		DoneX						;
      movlw		0x03						;
      movwf		R9						;
      movlw		0xDF						;
      call		pauseUSL					;
      goto		DelayXX						;
      clrf		R9						;
    pauseUSL							;
      addlw		0xE8						;
      movwf		R0						;
      comf		R9		,F				;
      movlw		0xFC						;
      btfss		status		,C				;
      goto		XpauseUSL					;
    pauseX								;
      addwf		R0		,F				;
      btfsc		status		,C				;
      goto		pauseX						;
    XpauseUSL							;
      addwf		R0		,F				;
      clrwdt							;
      incfsz	R9		,F				;
      goto		pauseX						;
      btfsc		R0		,00				;
      goto		pausedoneX					;
    pausedoneX							;
      btfss		R0		,01				;
      goto		pausedone					;
      goto		Done						;
    or on chip-EEPROM Read/Write:

    Code:
    EEPROMread							;read byte from on-chip EEPROM
      bsf		status		,rp0				;for bank 1
      movwf		EEADR						;set the EEPROM address
      bsf		EECON1		,0x0				;EECON1 in bank 3
      movf		EEDATA		,W				;read from data memory
      goto		DoneX						;done
    
    EEPROMwrite							;write byte to on-chip EEPROM
      bsf		status		,rp0				;for EE in bank 1
      movwf		EEDATA						;set the EEPROM data
      bsf		EECON1		,02				;
      movlw		0x55						;unlock the door
      movwf		EECON2						;
      movlw		0xAA						;
      movwf		EECON2						;
      bsf		EECON1		,01				;do the write
    writeloop							;
      btfsc		EECON1		,01				;wait for the write to complete
      goto		writeloop					;
      bcf		EECON1		,02				;lock up when we're done
      goto		DoneX						;
    So bottom line is if you are using any of these, insert them in your code once, straight away
    before bothering with timing, or determining which bank you want your variables to be in.
    Then you can add additional identical commands without worrying about anything else being added.
    All of these commands reuse the code from the first time they were used in a PBP program.
    Cheers, Art.

  22. #62
    Join Date
    Oct 2005
    Location
    Sweden
    Posts
    3,517


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Hi Art,
    I know most of that, the thing I'm having proplem with is this
    You want to keep most called functions (PBP routines) in the first 2K code space to avoid page switching.
    If the calling line (the GOSUB in your "main" routine) ends up in Page 1 while the sub is in Page 0 it STILL needs to switch pages - that's what I'm saying.

    But...Darrel just responded to the post on the MELABS forum with some details and it turns out that GOSUBing from Page 1 to Page 0 does indeed take one instruction less than the other way around - go figure. But (again) if everything fits within the same page (Page 0) then that same GOSUB now takes 3 instructions instead of 2. Go figure...

    /Henrik.

  23. #63
    Join Date
    Aug 2003
    Posts
    985


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    I always thought the PBP author put his routines closest to zero vector
    for the reason I gave. Now, since you sorted me out on that,
    I think it's to avoid bank or page switching in his asm code to both
    make it smaller, and if he didn't always know the internal variables were in bank0,
    timings of the routines would be a pain, just as it can be here.

    If the calling line (the GOSUB in your "main" routine) ends up in Page 1 while the sub is in Page 0 it STILL needs to switch pages - that's what I'm saying.
    There are often only a few loops where timing is an issue, like in the first example of this thread.
    or, for example, something that is sending or receiving bytes at a time in a for next loop can be
    called from anywhere and contained in the first 2K.

    Page 1 to Page 0 does indeed take one instruction less than the other way around - go figure.
    I haven't found the post, but it's cheaper to write a zero value than anything else,
    that is done with a single clrf instruction, but writing a one takes two instructions.

    if everything fits within the same page (Page 0) then that same GOSUB now takes 3 instructions instead of 2. Go figure.
    That one's got me stumped. I would like to see the disassembly.
    A jump from page 0 to page 0 should just be a gosub as if you are using a 2K chip.
    You'll notice in the code above there are no asm gosubs.
    Only returns to the gosubs that called the routines.
    I think they must be more expensive, but that doesn't explain the difference.

  24. #64
    Join Date
    Nov 2003
    Location
    Greece
    Posts
    3,795


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Quote Originally Posted by HenrikOlsson View Post
    if everything fits within the same page (Page 0) then that same GOSUB now takes 3 instructions instead of 2. Go figure...
    I think it is because it does not know if it is in page 0 or 1 or else, so a test must be done first?

    Ioannis

  25. #65
    Join Date
    Oct 2005
    Location
    Sweden
    Posts
    3,517


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Hi,
    Here's a link to the thread on MELABS forum. Darrel posted code there which he used to demonstrate, I'm sure you can disassemble that.

    /Henrik.

  26. #66
    Join Date
    Jan 2009
    Location
    Miami, Florida USA
    Posts
    637


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Quote Originally Posted by HenrikOlsson View Post
    Hi,
    Here's a link to the thread on MELABS forum. Darrel posted code there which he used to demonstrate, I'm sure you can disassemble that.

    /Henrik.
    Hmm, I knew that the used programming space goes down, but I had no idea that it had to do with the GOSUBs. Also, it is good to know that the enhanced chips do not have this issue.
    "No one is completely worthless. They can always serve as a bad example."

    Anonymous

  27. #67
    Join Date
    Oct 2012
    Posts
    81


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Hi Team,

    I am using the setup from post #43 and I need a clarification on how the duty cycle setting works.
    If I understood the data sheet correctly for a 16 MHz main clock and an output frequency of 250 KHz I have access to 16 steps of duty cycle.
    Also the manual states that you can use CCPR1L which is 8 bit wide and CCP1CON.5 plus CCP1CON.4 so you have access to a 10 bit wide setting.

    My question is who keeps track of individual values and their place in the 10 bit variable.
    Is the user supposed to do the logic or PBP takes care of it?
    For example if I use something like this:

    CCPR1L = 5
    CCP1CON.5 = 1 (an 0 means 0 and an 1 means 2)
    CCP1CON.4= 0 (an 0 means 0 and an 1 means 1)

    Is the result 7 so we just add the two values or is it 21 which comes from 5 shifted twice and add 2 from CCP1CON.5 ?

    Does one have to pick only multiple of 4 when choosing CCPR1L or whatever value is given is taken as a 10 bit value and added to CCP1CON 4 and 5?


    Regards,

    Nick

  28. #68
    Join Date
    Oct 2005
    Location
    Sweden
    Posts
    3,517


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Hi,
    With 16MHz main clock there are three different prescaler ratios all giving you 250kHz but different number of bits of resolution.
    If you set prescaler to 1:2 and load PR2 with 3 then you'll get 250kHz and 5 bits of resolution (not 5 "full" bits actually), ie you can set the dutycycle value anywhere between 0 and 16.

    If you set the prescaler to 1:1 and load PR2 with 15 you'll get the same frequency but now you've got better resolution, 0-64 instead of 0-16.

    Now, just write out whatever value you want in binary as a 10bit value: %0000010110
    The two least significant bits goes to CCP1CON.5 and CCP1CON.4 and the remaining 8 bits goes to CCPR1L, in this case (as in your example) the result would be 21 which would result in either 100% or ~20% depending on the prescaler and PR2 setting as outlined above.

    /Henrik.

  29. #69
    Join Date
    Oct 2012
    Posts
    81


    Did you find this post helpful? Yes | No

    Default Re: Maximum frequency output from a PIC

    Thank you Henrik.
    It makes more sense to me now.

    Regards,

    Nick

Similar Threads

  1. internal TMR for frequency output
    By Samoele in forum mel PIC BASIC Pro
    Replies: 0
    Last Post: - 15th January 2009, 10:38
  2. How to calculate PIC sampling frequency
    By minmin in forum General
    Replies: 1
    Last Post: - 26th September 2006, 19:02
  3. Replies: 2
    Last Post: - 20th January 2006, 22:09
  4. Maximum frequency count on 16F628/4MHz
    By solara in forum mel PIC BASIC Pro
    Replies: 10
    Last Post: - 23rd May 2005, 11:38
  5. Low frequency output
    By barkerben in forum General
    Replies: 5
    Last Post: - 16th November 2004, 16:25

Members who have read this thread : 1

You do not have permission to view the list of names.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts