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long delay time with 16f84a

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fs789

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please,
can any one help me to obtain along delay time 18 hours with pic16f84a and acrystal of 4MHZ ? i need the time to be accurate.

---------- Post added at 13:05 ---------- Previous post was at 11:36 ----------

please help me

---------- Post added at 13:06 ---------- Previous post was at 13:05 ----------

please help me to solve the problem
 

Tahmid

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Which language and compiler do you use?
In mikroBASIC we could do something like:
Code:
dim x as word
for x = 1 to 60000
   delay_ms(1080)
next x

That's a delay of 1.08 seconds 60000 times = 64800s = 1080mins = 18 hours

In mikroC, we'd do something similar.

Hope this helps.
Tahmid.
 
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fs789

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Which language and compiler do you use?
In mikroBASIC we could do something like:
Code:
dim x as word
for x = 1 to 60000
   delay_ms(1080)
next x

That's a delay of 1.08 seconds 60000 times = 64800s = 1080mins = 18 hours

In mikroC, we'd do something similar.

Hope this helps.
Tahmid.
i want to use assembly language , mplab program
 

keith1200rs

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I would use the built in timers to get the lowest frequency then use software counters to count multiples of that time period. Think of it as counting hours, minutes, seconds, hundredths of seconds, for example.

Keith.
 
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Tahmid

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Hi,
In that case, use the timer as keith suggested to get the longest delay. Calculate how long the delay is and according keep a seconds register that increments and resets accordingly in the process incrementing a minutes and an hours registers. When the value in the hours registers = 18, stop the timer and go on doing whatever you would.

Alternately a simpler method is the delay routine:
Code:
; Delay = 64800 seconds
; Clock frequency = 4 MHz

; Actual delay = 64800 seconds = 64800000000 cycles
; Error = 0 %

	cblock
	d1
	d2
	d3
	d4
	d5
	endc

Delay
			;64799999988 cycles
	movlw	0xA1
	movwf	d1
	movlw	0x24
	movwf	d2
	movlw	0x21
	movwf	d3
	movlw	0x60
	movwf	d4
	movlw	0x02
	movwf	d5
Delay_0
	decfsz	d1, f
	goto	$+2
	decfsz	d2, f
	goto	$+2
	decfsz	d3, f
	goto	$+2
	decfsz	d4, f
	goto	$+2
	decfsz	d5, f
	goto	Delay_0

			;8 cycles
	goto	$+1
	goto	$+1
	goto	$+1
	goto	$+1

			;4 cycles (including call)
	return

Hope this helps.
Tahmid.
 
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keith1200rs

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The choice between a delay or a timer depends on whether the processor needs to do anything in the 18 hours. If it does nothing for 18 hours then a delay is fine. If it needs to do anything during the 18 hours then you need to use a timer.

Keith.
 
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fs789

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thank you very much
please what do you mean by the term ($+1) ??
because i am newer in assemply language.
 

Tahmid

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Hi,

$ represents the current instruction.
So,
Code:
here: goto $
means
Goto current instruction, in other words, stay on that line

$+1 means next instruction.
$+2 means the instruction after the next one
$-1 means next instruction
$-2 means the instruction before the previous one

eg.
Code:
here:
bsf portb,1
bsf portb,2
goto $+2
bsf portb,3
bsf portb,4
goto $-5
Here, the lines are executed and then goes to "goto $+2", ie, it jumps to "bsf portb,4" then goes to "goto $-5" ie 5 lines before, ie "bsf portb,1"

Hope this helps.
Tahmid.
 
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fs789

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Hi,
In that case, use the timer as keith suggested to get the longest delay. Calculate how long the delay is and according keep a seconds register that increments and resets accordingly in the process incrementing a minutes and an hours registers. When the value in the hours registers = 18, stop the timer and go on doing whatever you would.

Alternately a simpler method is the delay routine:
Code:
; Delay = 64800 seconds
; Clock frequency = 4 MHz

; Actual delay = 64800 seconds = 64800000000 cycles
; Error = 0 %

	cblock
	d1
	d2
	d3
	d4
	d5
	endc

Delay
			;64799999988 cycles
	movlw	0xA1
	movwf	d1
	movlw	0x24
	movwf	d2
	movlw	0x21
	movwf	d3
	movlw	0x60
	movwf	d4
	movlw	0x02
	movwf	d5
Delay_0
	decfsz	d1, f
	goto	$+2
	decfsz	d2, f
	goto	$+2
	decfsz	d3, f
	goto	$+2
	decfsz	d4, f
	goto	$+2
	decfsz	d5, f
	goto	Delay_0

			;8 cycles
	goto	$+1
	goto	$+1
	goto	$+1
	goto	$+1

			;4 cycles (including call)
	return

Hope this helps.
Tahmid.
can you please explain for me how you calculated number of cycles and the value of delay??
 

Tahmid

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fs789

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thank you very much
can you please help me with this code?? it is simple delay loop,((i think about 585225 cycles)) is it true??
the problem is , the output port(B0) is flickering !!!!!!!!!!
ido not know the problem??

PROCESSOR 16f84a ; Defining processor
#include "p16f84a.inc" ; Microchip INC database
__CONFIG _CP_OFF & _WDT_OFF & _PWRTE_ON & _XT_OSC
; frequency 4MHZ
org 0x00
goto first


first bsf 03,5
bsf 81,7; ;81 option reg.
clrf 85 ; 85 and 86 are trisa, trisb
clrf 86 ; 03 is status
bcf 03,5
movlw .255
movwf 0f
clrf 05 ; 05 port a and 06 port b
clrf 06
delay bsf 03,0
movlw d'255'
movwf 0c
movwf 0e
movwf 0d
decfsz 0c,f
goto $-1
bsf 03,0
decfsz 0d,f
goto $-1
bsf 03,0
decfsz 0e,f
goto $-1
bsf 03,0
decfsz 0f,f
goto delay
bsf 06,0
end
 
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Tahmid

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Hi,

From "first bsf 03,5" to end, it's 588271 cycles. Use the MPLAB stopwatch tool to find it out.

Hope this helps.
Tahmid.

---------- Post added at 16:30 ---------- Previous post was at 14:49 ----------

Hi,
You added the include file, so you can use the names of the SFR instead of the locations. eg:
Code:
first bsf 03,5
can now be written as
Code:
first bsf STAUS, 5
or
Code:
first bsf STAUS, RP0

Code:
clrf 85 ; 85 and 86 are trisa, trisb
can be written as
Code:
clrf TRISA

You just need to be careful that the names of the SFR are written in capital letters.

Hope this helps.
Tahmid.
 
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fs789

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ok. thank you
is my code has any mistakes??
and why when i connect pic in real application, the output seems flickering??not stable
 

Tahmid

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Hi,
I haven't gone through the code, but there maybe other reasons the output is flickering.
Most common I would say is inappropriate supply line filtering. Very near the PIC power pins(VDD and VSS) place a 0.1uF ceramic capacitor and a 100uF electrolytic along the power line. This should get rid of spikes/noise problems that can affect the PIC.
Then, check if your oscillator is placed near the PIC. Having the oscillator very far away and connecting it to the PIC may also result in unwanted behaviour.

I'll see the code to see if it's ok.

Hope this helps.
Tahmid.
 
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fs789

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HI,
i have checked the connection of circuit,oscillator,capacitors,and every thing is ok.
but the problem of fkickering is still happening!!!!!!!!!!
 

Tahmid

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This is the corrected version of your code:
Code:
PROCESSOR 16f84a ; Defining processor
#include "p16f84a.inc" ; Microchip INC database
__CONFIG _CP_OFF & _WDT_OFF & _PWRTE_ON & _XT_OSC
; frequency 4MHZ
org 0x00
goto first


first bsf 03,5
bsf 81,7; ;81 option reg.
clrf 85 ; 85 and 86 are trisa, trisb
clrf 86 ; 03 is status
bcf 03,5
movlw .255
movwf 0f
clrf 05 ; 05 port a and 06 port b
clrf 06
delay bsf 03,0
movlw d'255'
movwf 0c
movwf 0e
movwf 0d
decfsz 0c,f
goto $-1
bsf 03,0
decfsz 0d,f
goto $-1
bsf 03,0
decfsz 0e,f
goto $-1
bsf 03,0
decfsz 0f,f
goto delay
bsf 06,0
goto $
end

The error here is after ~589ms, the microcontroller turns PORTB0 on and then the program ends, causing the microcontroller to jump to start and restart everything including all initializations. This is undesirable. What you want is to make the microcontroller sit idle and not end the program so that it does not restart.
That's why before end, I made the microcontroller endlessly loop there, such that it never restarts again. It is done by placing:
Code:
goto $
before end.

A more organised and easy to read and understand version of your code would be such:
Code:
PROCESSOR 16f84a ; Defining processor
#include "p16f84a.inc" ; Microchip INC database
__CONFIG _CP_OFF & _WDT_OFF & _PWRTE_ON & _XT_OSC
; frequency 4MHZ
	CBLOCK 0X0C	
		COUNT,D1,D2,D3,D4
	ENDC

	org 0x00
	goto first


first 
	clrf	PORTA
	clrf	PORTB
	bsf 	STATUS,RP0
	bsf 	OPTION_REG,7; ;81 option reg.
	clrf 	TRISA ; 85 and 86 are trisa, trisb
	clrf 	TRISB ; 03 is status
	bcf 	STATUS,RP0
	movlw 	.255
	movwf 	COUNT

delay
	bsf 	STATUS,0
	movlw 	.255
	movwf 	D1
	movwf 	D3
	movwf 	D2
	decfsz 	D1,f
	goto 	$-1
	bsf 	STATUS,0
	decfsz 	D2,f
	goto 	$-1
	bsf 	STATUS,0
	decfsz 	D3,f
	goto 	$-1
	bsf 	STATUS,0
	decfsz 	D4,f
	goto 	delay

	bsf 	PORTB,0
	goto	$
end
This makes it easy to understand your code. I hope you understand the differences.

Hope this helped.
Tahmid.

---------- Post added at 17:25 ---------- Previous post was at 17:24 ----------

I have simulated both the codes and they are working properly.
 
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THANK YOU VERY MUCH
but now ,assume i want adelay time 18 hours.
the code is generated as follows :
is this time is very accurate??? if use this this delay every day,what do yoy expect the error ,(accumulating error) in ayear??
the code is as follows:

; Delay 64 800 000 000 machine cycles
; Duration of the delay 18 hour
; Frequency of the pulsing oscillator 4 MHZ

movlw .157
movwf Reg_1
movlw .14
movwf Reg_2
movlw .113
movwf Reg_3
movlw .3
movwf Reg_4
movlw .6
movwf Reg_5
decfsz Reg_1,F
goto $-1
clrwdt
decfsz Reg_2,F
goto $-4
decfsz Reg_3,F
goto $-6
decfsz Reg_4,F
goto $-8
decfsz Reg_5,F
goto $-.10
nop
nop
 

Tahmid

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Hi,
The 18 hour delay is perfect, but what would likely make the circuit inaccurate, would be crystal frequency, deviation over time and temperature and more importantly how much time you are losing by calling the delay and doing other stuff.

Hope this helps.
Tahmid
 

fs789

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Hi,
The 18 hour delay is perfect, but what would likely make the circuit inaccurate, would be crystal frequency, deviation over time and temperature and more importantly how much time you are losing by calling the delay and doing other stuff.

Hope this helps.
Tahmid
OK, THANK YOU .
IF ALL THESE FACTORS( TEMPERATURE,crystal frequency, deviation over time......) HAPPENED: WHAT IS THE DEGREE OF ACCURACY DO YOU THINK WE WILL HAVE IN THIS SITUATION??
IS IT ACCEPTABLE ??
 

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