How to start PIC16F676 ...??

[ericgibbs]

hi Ian,
Sent you a PM about 1hr ago, ref this ADC setup problem on OSH.

E.

 

[Ian Rogers]

0x3D14 IS only 14 bits!! 11 - 1101 - 0001 - 0100. the ' D' really should be 1 as bits 12,11 and 10 are unused..

 

[koolguy]

I want to clear this why there is double __ underscore???
__config 0x3D14

 

[koolguy]

so, we are using this Oscillator:-
100 = INTOSC oscillator: I/O function on RA4/OSC2/CLKOUT pin, I/O function on RA5/OSC1/CLKIN

and

MCLRE: RA3/MCLR pin function select(5)
1 = RA3/MCLR pin function is MCLR

what does this mean?

bit 13-12 BG1:BG0: Bandgap Calibration bits for BOD and POR voltage(1)
00 = Lowest bandgap voltage
11 = Highest bandgap voltage

 

[Ian Rogers]

New code for you ritesh..... Put this into oshonsoft assembler it works ok now

	;include "P16F676.inc"		;include the defaults for the chip
	__config 0x3114			;sets the configuration settings (oscillator type etc.)
							; HERE SET TO INTERNAL OSCILLATOR 4MHZ
	ORG 0
	GOTO INIT
 
INIT
	CLRF OPTION_REG
	BSF STATUS,RP0
	CLRF VRCON
	MOVLW 0x3f
	MOVWF TRISA 	; porta as input
	MOVLW 0x0
	CLRF ANSEL 	; disable ADC
	MOVWF TRISC 	; portb as output
	BCF STATUS,RP0
	MOVLW 0x7
	MOVWF CMCON
 
START
 
	btfss PORTA,1 	; test bit 1
	call delay
 
	GOTO START
 
delay
	movlw 0xff
	movwf PORTC 
	movlw 0fh
	movwf 0x21
	dECfsz 0x21,f
	clrf PORTC
	RETURN
 
end

Band gao voltage associated with BOD & POR Brown Out Detect and Power On Reset Read section 9.3.5 on this topic.

 

[koolguy]

Thanks the code are working ...

ORG 0
GOTO INIT

What the need of this can't we start normally?
please explain more this part of code...

CLRF OPTION_REG??
CLRF VRCON??

 

[Ian Rogers]

please explain more this part of code...

CLRF OPTION_REG??
CLRF VRCON??

I was just trying to find out why the ADC wasn't being turned off.

VRCON is for the voltage reference module (it's unused, so I disabled it)
OPTION_REG has interrupt settings so I disabled them all.

ORG 0
GOTO INIT

Try to get into the habit of including this. When you use tables and interrupts you'll need to jump over them.

 

[ericgibbs]

Sticky.

 

[koolguy]

Please clear one more doubt __config why two underscore not single is that also set in data sheet??

 

[Ian Rogers]

__config is a makro.. written by someone in microchip... To know why there is two underscores you'll need to find him and ask him.

Usually the underscore is used in C for assembler routines... purely for keeping identifiers apart.... If it was declared just config... It would mean no-one could use this identifier.

The datasheet may well have two, its depends on the font used.

Sorry... Its a directive for the assembler / linker, not a makro.....

 

[koolguy]

Hi,

Please explain the function of bit 3, i am not getting its working.
MOVLW 0x7
MOVWF CMCON


19h CMCON — COUT — CINV CIS CM2 CM1 CM0

bit 3 CIS: Comparator Input Switch bit
When CM2:CM0 = 110 or 101:
1 = VIN- connects to CIN+
0 = VIN- connects to CIN

 

[Ian Rogers]

Look at figure 6.2 Comparator i/o operating modes.... CIS in the last two configurations (this is where VRCON comes in).

 

[koolguy]

Here it is but my doubt is not clear.....

 

[koolguy]

In the above code i don't understand if the decrement is not working what the need of it??
movlw 0fh
movwf 0x21
dECfsz 0x21,f

 

[koolguy]

I have done some changes in delay for LED remain glowing for few seconds..
But the OSHON shows HARDWARE STACK OVERFLOW after running simulator.

;include "P16F676.inc"		;include the defaults for the chip
	__config 0x3114			;sets the configuration settings (oscillator type etc.)
							; HERE SET TO INTERNAL OSCILLATOR 4MHZ
	ORG 0
	GOTO INIT
 
INIT
	CLRF OPTION_REG
	BSF STATUS,RP0
	CLRF VRCON
	MOVLW 0x3f
	MOVWF TRISA 	; porta as input
	MOVLW 0x0
	CLRF ANSEL 	; disable ADC
	MOVWF TRISC 	; portb as output
	BCF STATUS,RP0
	MOVLW 0x7
	MOVWF CMCON
 
START
 
	btfss PORTA,1 	; test bit 1
	call delay
 
	GOTO START
 
delay
	movlw 0xff
	movwf PORTC 
	movlw 0fh
	movwf 0x21
again:	dECfsz 0x21,f
	call again
	clrf PORTC
	RETURN
 
end

 

[ericgibbs]

hi Ritesh,

[B]again[/B]:	dECfsz 0x21,f
	[B]call again[/B]
	clrf PORTC
	RETURN

Your code is wrong, its calling itself, so it will over flow the STACK

 

[koolguy]

The code given by IAN also is not working this part the F is decremented to E only....!!

movlw 0fh
movwf 0x21
dECfsz 0x21,f
clrf PORTC
from:->

	;include "P16F676.inc"		;include the defaults for the chip
	__config 0x3114			;sets the configuration settings (oscillator type etc.)
							; HERE SET TO INTERNAL OSCILLATOR 4MHZ
	ORG 0
	GOTO INIT
 
INIT
	CLRF OPTION_REG
	BSF STATUS,RP0
	CLRF VRCON
	MOVLW 0x3f
	MOVWF TRISA 	; porta as input
	MOVLW 0x0
	CLRF ANSEL 	; disable ADC
	MOVWF TRISC 	; portb as output
	BCF STATUS,RP0
	MOVLW 0x7
	MOVWF CMCON
 
START
 
	btfss PORTA,1 	; test bit 1
	call delay
 
	GOTO START
 
delay
	movlw 0xff
	movwf PORTC 
	movlw 0fh
	movwf 0x21
	dECfsz 0x21,f
	clrf PORTC
	RETURN
 
end

 

[ericgibbs]

hi


delay
movlw 0xff
movwf PORTC
movlw 0fh
movwf 0x21; you are reloading 0x21 with 0Fh
dECfsz 0x21,f; DEC by 1 count
clrf PORTC ; clearing PORTC.
RETURN; now returning!!!

The decfsz is NOT being used a Conditional Instruction!!

 

[koolguy]

The decfsz is NOT being used a Conditional Instruction!!

Hi again,

Then i think there is no use of it!!

 

[Nigel Goodwin]

Hi again,

Then i think there is no use of it!!

As we've told you repeatedly - READ THE DATASHEET!! - there's only 35 odd instructions, it's hardly difficult.

The obvious one you SHOULD have used is 'decf'.