Test and branch code

[AGCB]

Would someone look at this branching code and tell me if there is something wrong.
What I'm trying to do is receive a message from another PIC via USART and then branch accodingly. I have simplified my actual code so you can understand it w/o the whole program. I'm using 18 series chips for both send and receive.

usart_in	
	
	movf	rcreg,w		;get info into wreg	
	
	cpfslt	number		;if number (0xf9) is less than wreg,(I.E. W is greater)
				;	 skip next instruction
	bra	set_A
			
	sublw	0xfa		;if wreg is 0xfa		
	btfsc	status,z	;
	bra	Set_B		;yes, Z is set	
	
	
	sublw	0xfb		;if wreg is 0xfb		
	btfsc	status,z	;
	bra	Set_C		;yes, Z is set

		;other tests for 0xfc-0xff

return

I have reserved 0xfa-ff for instructions. Everything below 0xfa will be displayed as a 3 digit decimal. It works until I add the FB test, then seems to reset or go back to the front of program. I have tried both using interrupts and just polling the receive flag RCIF. The USART part works fine.

 

[Pommie]

If you have already subtracted 0xfa from W then to check for 0xfb only requires you to subtract 1 more. Alternatively, reload W before the second subtract.

Mike.

 

[AGCB]

If you have already subtracted 0xfa from WMike.

You know, as I was getting into bed last night, I thought of the fact that W may be changed before the 2nd test, and your reply and my looking at the datasheet this morning confirmed that.
Thanks Mike

 

[AGCB]

Just one more confirmation of my understanding. On the instructions CPFSEQ/GT/LT the contents of the wreg is not changed by these instructions. Am I right?

 

[Mike - K8LH]

Just one more confirmation of my understanding. On the instructions CPFSEQ/GT/LT the contents of the wreg is not changed by these instructions. Am I right?

Yes, that's correct...

 

[Mike - K8LH]

So are you branching to Set_A if RCREG <= 0xF9 and the other sets for 0xFA through 0xFF? Something like this?

test    movf    RCREG,W         ; get RX data
        sublw   0xF9            ; data >= 0xFA?
        skpnc                   ; yes, skip, else
        bra     Set_A           ; branch ( rcreg <= 0xF9)
        infsnz  WREG,W          ; 0xFA? no, skip, else
        bra     Set_B           ;
        infsnz  WREG,W          ; 0xFB? no, skip, else
        bra     Set_C           ;
        infsnz  WREG,W          ; 0xFC? no, skip, else
        bra     Set_D           ;

 

[AGCB]

So are you branching to Set_A if RCREG <= 0xF9 and the other sets for 0xFA through 0xFF? Something like this?

test    movf    RCREG,W         ; get RX data
        sublw   0xF9            ; data >= 0xFA?
        skpnc                   ; yes, skip, else
        bra     Set_A           ; branch ( rcreg <= 0xF9)
        infsnz  WREG,W          ; 0xFA? no, skip, else
        bra     Set_B           ;
        infsnz  WREG,W          ; 0xFB? no, skip, else
        bra     Set_C           ;
        infsnz  WREG,W          ; 0xFC? no, skip, else
        bra     Set_D           ;

I believe your code and mine accomplish the same, provided I reload W before each test as POMMIE said. Short answer, Yes. That part of my code has been corrected but still have a problem. I will start a new thread as the title of this one doesn't apply. See 'Computed GOTO jumps back one byte"