no branch instructions in pic16f877a

[JAMAL JIMI]

Hi everybody......
I am trying to program pic16f877's ADC but there is no branch instruction in the instruction set.....
So how can I display the ADC result on the LCD in the form of numbers?????

Plzzzzzz help me.....

 

[bigdogguru]

The BTFSS and BTFSC provide a means of conditional jumps:


Simple PIC Conditional Jump Using BTFSC

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Code ASM - [expand]
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;
 
include p16f877.inc ;Include file for register definitions
 
; ************************************************************
; equates
 
count equ 0x25 ;Manually assign register address!
 
; ************************************************************
; start at the reset vector
 
org 0x000 ; Set origin at memory address 000
nop ; very important - required for debugger
 
Start bcf STATUS,RP0 ; go to BANK 0 by setting
bcf STATUS,RP1 ; RP1:RP0 to 0 0.
 
; Initialize contents of variables.
;
 
movlw 0x0A ; Initialize count to 10 decimal by
movwf count ; setting W and moving W -> count.
 
;
; Do the simple loop.
 
loop decf count,F ; count = count - 1.
btfsc STATUS,Z ; Skip next instruction if Z=0.
stop goto stop ; End program.
goto loop ; Continue looping!
 
End

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BigDog

 

[JAMAL JIMI]

Dear I wasn't mean that........ I want to say that if, for example, i have some specific value in the ADC result register and i want to use that value to display a specific number on the lcd then what will i do............for example in 89c51 with an external 8 bit ADC connected to port1 i can display its value with the help of these instructions............

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Code ASM - [expand]
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org 0h
                    mov a,#0ffh
                    mov p1,a             ;make p1 as input port
again:            mov r1,p1            ;move p1 value to r1
                    mov a,#0afh
                    cjne r1,a,again     ;if equal diplay 24 on the lcd
                    lcall dis24
                    ..........
                    ........
                    .....
dis24:
 
                    ;commands for displaying 24 on the lcd
                    ..........
                    .............
                    .........
                    ret
                    end

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[jpanhalt]

If you want to display a specific something, such as a number or text string, based on something else, such as an ADC value, then you do a conditional branch as BigDog shows. I would be cautious and probably set the trigger ADC value to a range or to a greater than/less than flag (i.e. test the ADC value, if it meets that test, then set a flag bit in a flag register, then test that flag bit for the conditional branch). BigDog's example uses the zero bit of the Status register as a flag. I usually have just a "flag" register in addition that gives me 8 bits to check for various conditional branches, if needed.

@BigDog: Does your jump to "stop" (i.e., goto stop) compile?

John

 

[bigdogguru]

@John

Actually, it is not my code, I simply found the example during a quick search.

However, I see no reason why it shouldn't compile.

It basically puts the execution flow into an endless loop.

Perhaps if I find the time I'll attempt to assemble it.


@Jamal

Rather than posting additional examples, perhaps you should examine the following Gooligum tutorials in PDF form with downloadable source code:

MPLAB based IDE

**broken link removed**

**broken link removed**


MPLAB X based IDE

**broken link removed**

**broken link removed**


The tutorials are actually quite good covering both the Baseline and Midrange PIC Programming in Assembly and C using both the original MPLAB and the newer MPLAB X IDEs.

I would recommend studying the first two tutorials, they cover the majority of PIC Assembly Language required to master the topic.


BigDog

 

[wp100]

Hi,

Think you mean like this ..?

; 		adc routine result in ADRESH lower 2 bits ignored

		movlw	0xAF  ; reference value

		subwf	 ADRESH

		btfsc	STATUS,Z
		goto	lcd_output   ; is equal

		btfsc	STATUS,C
		goto	lcd_output   ; ADRESH is greater

 

[JAMAL JIMI]

Thanks dear now i understand..............its so simple...