Is " xorlw '$' " valid opcode for a PIC?

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johankj

New Member
I saw this code for a PIC (16F88) using RS232 to receive GPS data.

All GPS data has a string identifier at the start of the sentence $, followed by for example $GPRMC.

Here is the code in question
Code: 
		;Sit here waiting around until you get a valid start of a NMEA sentence	
		movfw	Rcd_Char
		xorlw	'$'				;start of sentence?

Rcd_Char I assume is the received character, which is moved to W. Then, presumably, xorlw '$' will maske W, and return zero.

WOT? Have I've been doing hours of ASCII to binary conversions all for nothing? When I could've done:
Code: 
	MOVLW	'A'
	CALL	RS232_SEND
 
johankj said:
WOT? Have I've been doing hours of ASCII to binary conversions all for nothing? When I could've done:
Code: 
	MOVLW	'A'
	CALL	RS232_SEND
Click to expand...

Yes you have, perhaps you should have read the assembler instructions or helpfile?. You can declare constants as decimal, hex, binary, ASCII - and perhaps even octal? (never been interested enough to find out).
 
Nigel Goodwin said:
Yes you have, perhaps you should have read the assembler instructions or helpfile?. You can declare constants as decimal, hex, binary, ASCII - and perhaps even octal? (never been interested enough to find out).
Click to expand...

Ouch! Ok, by declaring constants, do you mean something like?:
Code: 
#DEFINE		A	B'O1100101'

	...


	MOVLW		A
	CALL		RS232_SEND
 
Ok, I just looked up the .hpl file that came with MPASM.

I seems you can use the following syntax for ASCII

A'A'

or just

'A'

So just scratch that above comment Thanks for the comment Nigel.
 
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