hex question

[Ambient]

This is probably a dumb question, but I could not find a reasonable explanation after hours of searching. When do I use 0x prefix and when do I use 0000h? I keep seeing both appear in the same program, and all the tutorials I can find do not explain the difference. I know both are hex. I mostly see the 0x prefix for addresses, but have also seen it in variable declarations. Can someone clear up my confusion?

 

[Gayan Soyza]

You can use both which one do you like?

0x00 & 00h both are same

0x0000 & 0000h are same

If you want to move literal ‘0’ then Simply do

Movlw 00h
Movwf PORTB

Or

use clrf PORTB

 

[Ambient]

Thanks. I just wasn't sure if MPLAB needed a specific form of hex label for the instructions to work.

 

[Gayan Soyza]

If you are confusing with the hex numbers
Let say you want to move DECIMAL 50 to PORTB. But you don’t know what’s the exact HEX value for decimal 50.

Then you can write

	Movlw D.50
	Movwf PORTB

But the actual HEX value for DECIMAL 50 is 32h.

3 X 16 + 2 = 50

MPLAB Text Editor is a powerful tool it detects any number in any manner which you input it by DECIMAL, HEX, BINARY etc…

For more information about the hex number system go through this link.

**broken link removed**

 

[Papabravo]

The two methods of representing a hexadecimal constants come from different origins. The 'h' suffix was popular in assemblers for intel microprocessors in the early 1970s. The assemblers for the 8008, 8080, and 8085 all had this feature. The 0x notation appears to have made its appearence with the K&R C compiler in the late 1970's. Since that time many assembler writers have made both forms of expression acceptable since we no longer have the memory limitations of the early 1970s. Curiously the compiler writers do not seem to have returned the favor. I guess we can chalk that up to standards committees.

 

[Pommie]

If you are confusing with the hex numbers
Let say you want to move DECIMAL 50 to PORTB. But you don’t know what’s the exact HEX value for decimal 50.

Then you can write

	Movlw D.50
	Movwf PORTB

I thought decimal 50 could be either .50 or d'50' not d.50.


Mike.

 

[Gayan Soyza]

Oh yes it was my mistake.It should be

	Movlw d'50'
	Movwf PORTB

Thanks

 

[Nigel Goodwin]

The various different number formats are explained in the MPASM/MPLAB help file, to make the assembler as versatile as possible, it accepts HEX in a number of different styles - as suggested, these vary according to your programming heritage.