Pic18f4550 adc

[adrianvon]

Hi,

The ADC that i made increment the binary value by 1 bit for every degree (i.e. 0degree =00000000B ... 1degree= 00000001B etc.). Now i want to display the Temperature on an LCD which means that i have to convert the digital value from the ADC (which is set to 7 bit) to ASCII. To do so, i am adding 48 decimal to the binary value.

The problem is that this method is only working fine for a single character (i.e. from 1 to 9). When the temperature gets higher (from 10 onwards), the LCD will display other characters instead of numbers. I know that this is caused since the ASCII table does not represent more that one character with 8 bits.

Is there a way that the values from the ADC which are above 9 be converted to ASCII ??

Thanks in advance,
Adrian

 

[ericgibbs]

hi adrian,
This is a simple demo, write the ascbfrs to the LCD as ASCII

;Byte to BCD or ASCII into ascbfr, from Byte in binvall

	list	p=16f876a
	#include <p16f876A.inc>

	errorlevel -302, -207

	__config _CP_OFF & _XT_OSC & _PWRTE_ON  & _WDT_OFF & _LVP_OFF



temp1	equ 	0x21
temp2	equ 	0x22
binvall equ 	0x23
binvalm equ	0x24

 
ascbfr2 equ 	0x40
ascbfr1 equ 	0x41
ascbfr0 equ 	0x42



	org 0x0000
	goto test
	org 0x0004
	retfie
	
test:
	movlw	.140
	movwf 	temp1
	addwf	temp1,w
	
trap:	goto trap


	movlw 	.123
	movwf	binvall
	call	bin2asc
	


;convert 8 bit bin to 3 asci in ascbfr0
bin2asc:
	clrf	ascbfr2
	clrf  	ascbfr1
	clrf	ascbfr0;lsd
	 	 
    	movlw   .8 
	movwf   temp1

bitloop:;shift msb into carry
    	rlf     binvall,F 
    	
    	movlw   ascbfr0	;0=lsd 1st
    	movwf   FSR	;fsr=pointer to digits
    	movlw   0X03	;digits to do
    	movwf   temp2
adjloop:
    	rlf     INDF,F	;shift digit 1 bit left
    	movlw   0X0A
    	subwf   INDF,W	;check and adjust for decimal overflow
    	btfsc   STATUS,C
    	movwf   INDF

    	decf    FSR,F;incf=msd 1st next digit
    	decfsz  temp2,F
    	goto    adjloop
    	decfsz  temp1,F;next bit
    	goto    bitloop

	;return from here if BCD only
	
    	movlw	0X30;make asci
	iorwf   ascbfr2,F
	iorwf   ascbfr1,F
	iorwf   ascbfr0,F
	return 

	end

 

[adrianvon]

Hi,
Thanks for the reply.

Why is .140 moved to register temp1 and .123 moved to register binvall ?? to be honest i cannot understand the coding very well since i never programmed a 16F.

 

[ericgibbs]

Hi,
Thanks for the reply.

Why is .140 moved to register temp1 and .123 moved to register binvall ?? to be honest i cannot understand the coding very well since i never programmed a 16F.

hi,
As I said, its a demo, this code is just dummy data, remove following fragment from the routine.
frag:
test:
movlw .140
movwf temp1
addwf temp1,w
trap: goto trap
movlw .123


You move the 7bit value you want to convert to ASCII into the binval register and then call bin2asc.

After the conversion is complete you will have 3 ASCII characters in these registers
ascbfr2 equ 0x40
ascbfr1 equ 0x41
ascbfr0 equ 0x42
Send them one at a time to the LCD character write subroutine
If you want to insert a decimal point in the displayed value do this.

Send ascbfr2, then ascbfr1, then decimal point "." , then ascbfr0

OK.?

 

[adrianvon]

Hi,

Thanks for explaining. I will try to do it later today.

 

[adrianvon]

Hi,

The program is giving errors.

RLF     BINVALL,F

rlf is not being recognized as an instruction, and are FSR and INDF registers ??

Thanks

 

[ericgibbs]

Hi,

The program is giving errors.

RLF     BINVALL,F

rlf is not being recognized as an instruction, and are FSR and INDF registers ??

Thanks

hi,
As you are using an 18F4550, just change the instructions from the 16F series to the equivalent 18F instruction, do you know how to do that.??

 

[adrianvon]

Hi,
Unfortunately i dont know how to do that. Is this done form the software itself ? or find the instructions from the datasheet ?

Thanks

 

[ericgibbs]

Hi,
Unfortunately i dont know how to do that. Is this done form the software itself ? or find the instructions from the datasheet ?

Thanks

hi,
Its in the datasheets, look at the Instruction Set section, if you get stuck , please ask.

 

[adrianvon]

Hi ,

I changed rlf with rlcf, FSR with FSR0 and INDF with INDF0. The program is recognizing them as instructions but its still not working, but i will try again tomorrow.

Thanks

 

[adrianvon]

Hi, i managed to do it. I used the coding in the link below:



The only problem is that i cannot understand how the conversion is being done. I would appreciate if someone can explain with comments how the conversion is being done.

Thanks in advance for your help.

 

[Ian Rogers]

Thats a confusing function.... Its named BIN2BCD.... when of course it isn't coding a decimal... Its just separating the binary number into hundreds, tens and units and adding 48 to each..

Ascii '0' is equal to 48 decimal ( as I'm sure you know ).

 

[ericgibbs]

Hi ,

I changed rlf with rlcf, FSR with FSR0 and INDF with INDF0. The program is recognizing them as instructions but its still not working, but i will try again tomorrow.

Thanks

hi adrian.
I have tidied the subr, it can be either a 16 or 8 bit conversion, see the comments.

;8 or 16 Bit Binary to 3 or 5 Ascii Routine for 18F4550   24May08    
;tested works OK.  redone 26/01/2012 OK


	list	p=18f4550,f=inhX32
	#include <p18f4550.inc>

	errorlevel -302, -207

 CONFIG PLLDIV=5,CPUDIV=OSC1_PLL2,USBDIV=2,FOSC=HSPLL_HS,IESO=OFF
 CONFIG VREGEN=ON,CCP2MX=ON,WDT=OFF,WDTPS=32768,PBADEN=OFF ,PWRT=OFF,MCLRE=ON
 CONFIG LPT1OSC=OFF,BOR=ON,BORV=2,STVREN=ON,LVP=OFF,ICPRT= OFF,XINST=OFF,DEBUG=OFF
 CONFIG WRTB=ON

Xtal SET 4

;AscBfrs for convert subr    
	AscBfr4	equ 0x060;; not needed for 8bit
	AscBfr3	equ 0x061;; not needed for 8bit
	AscBfr2	equ 0x062
	AscBfr1	equ 0x063
	AscBfr0	equ 0x064
		 
	BinValL	equ 0x068
	BinValM	equ 0x069;	not needed for 8bit

	No_Bits	equ 0x06B
	Digit_Cnt equ 0x06C


;-------------------
	org	0x0000
			
Main:
	movlw	.123;39h ;just for testing preload value 
	movwf	BinValL
	;;movlw	0;30h
	;;movwf	BinValM

	call	Bin2Asc
done:	
	goto	done;  Main


;Binary to Ascii conversion Subr  
;enter with BinValH and BinValL holding the [8] 16bit binary value to be converted.    
;exit with  [3] 5 Ascii value,,,, the BinValH/L is all '0' on exit    
;NOTE: to expand to a 16bit WORD and 5 ASCII character output, remove the ';;' before the
;intructions....
Bin2Asc: 	 
	;;clrf	AscBfr4		;clear buffers
	;;clrf	AscBfr3
	clrf	AscBfr2
	clrf	AscBfr1
	clrf	AscBfr0
	movlw	.8;;.16
	movwf	No_Bits
BitLoop: 	 
	rlcf	BinValL,F 
	;;rlcf	BinValM,F	;carry = msb < 1

	LFSR	FSR0,AscBfr0	;lsd 1st
	movwf	FSR0		;pointer to ascbfr 
	movlw	0X03;;05		;digits to do
	movwf	Digit_Cnt
AdjLoop: 	 
	rlcf	INDF0,F		;shift ASCII byte in [INDF0] 1 bit left
	movlw	0X0A		;decimal 10
	subwf	INDF0,W		;W=[INDF0]-10

	btfsc	STATUS,C	;skip if no carry,  its a negative result
	movwf	INDF0		;only save if postive result  

	movf	STATUS,W	;NB. the decf FSR0L sets Carry!
	decf	FSR0L,F		;point to next msd Ascbfr  
	movwf	STATUS		;recall Status from before the decf FSR0L

	decfsz	Digit_Cnt,F	;dec AscBfr counter
	goto	AdjLoop		;go next ascii

	decfsz	No_Bits,F
	goto	BitLoop		;go next bit shift left for BinVal

	movlw	0X30		;make asci
	;;iorwf	AscBfr4,F
	;;iorwf	AscBfr3,F
	iorwf	AscBfr2,F
	iorwf	AscBfr1,F
	iorwf	AscBfr0,F
	return

     
	end

 

[adrianvon]

Hi ericgibbs,

Thanks a lot for explaining the code

 

[adrianvon]

Hi, i am including two interrupt rourines to my coding, one high priority and a low priority interrupt. Now my question is, can i use goto instead of RETFIE ?? I want to use goto instruction since when the low priority interrupt is active, and the high priority interrupts it, when ready it will return to the low priority ISR. I dont want this to happen, instead i want it to go back to the MAIN label.

Thanks.

EDIT: I already tried using the GOTO instruction, but its not working.

 

[adrianvon]

Hi all,

As i said in previous posts, i want to display the temperate on an LCD. The LCD coding that is was using previously wasn't mine and it was to complex to understand, so i decided to do a new coding.

The tutorial im using is attached below and the coding used is of experiment 8.

When building the program (on MPLAB) it give no errors, but when programmed to the PIC, its not working. Can someone help me trouble-shooting the problem please. (attached is my coding)

Thanks in advance.

 

[ericgibbs]

Hi all,

As i said in previous posts, i want to display the temperate on an LCD. The LCD coding that is was using previously wasn't mine and it was to complex to understand, so i decided to do a new coding.

The tutorial im using is attached below and the coding used is of experiment 8.

When building the program (on MPLAB) it give no errors, but when programmed to the PIC, its not working. Can someone help me trouble-shooting the problem please. (attached is my coding)

Thanks in advance.

hi adrian,
The LCD is not being initialised correctly.

From your earlier posts I thought you had decided on a 4 bit LCD for Data.??

The pdf you posted shows a different connections for the LCD control.

 

[adrianvon]

Hi,

The problem was that the starting delay was too long, but now i have another problem. Instead of 'HELLO' the LCD is displaying 'HHHHH' (i.e. the first letter of HELLO for five times). Is this caused by 'ADDWF STATUS,F' instruction ??

Thanks

EDIT: Hi ericgibbs. I set the LCD to 8 bit mode since i have pins which are not being used.

 

[adrianvon]

and by the way, what is the difference between BRA and GOTO instructions? Is there a limit on how much the GOTO instruction can be used? and the CALL instruction, is there a limit on how much it can be used?

 

[Ian Rogers]

Branch and goto are immediate jumps... The PC is changed and that't that... you can do this as often as you like... Call however has a return address.... This has to be saved so the PC can continue after the call.... there are a few times this happens.... Call's... interrupt's.. Lookup's.... Interrupts require two stack positions... On a pic14 there are 8 positions in the stack... On the pic16 there are 16.

That governs the amount of nested calls you can make... I think you are using pic16 range.... pic18fxxxx, If so I would limit the nested calls to 14 (always keep two for an interrupt)