Bitwise not working

[Ioannis]

I know it is silly but cannot see why is not working the bitwise function. The code is:

for i=240 to 250
temp=portb
portb=temp & i
pause 100
next i

Port B high nibble is input while the low nibble is output. I read the whole port and want to keep the upper since they are related to Interrupt on change. So on the lower I want to follow the counting of i.

The lower nibble always reads and presents as 0000 !

If anyone sees what I don't please reply. It drives me mad!

Ioannis

[sayzer]

Hi Ioannis,

Here I made it clear to see.
But, as you said, it should not provide 0000.

Ignore high nibble on Portb. PORTB is just an example here.
.
.
i=240 to 250	11110000	11110001	11110010	11110011	11110100	11110101	11110110	11110111	11111000	11111001	11111010
PORTB (example)	11110000	11110001	11110011	11110111	11111111	11111110	11111100	11111000	11111010	11110101	11111101
Temp=PORTB	11110000	11110001	11110011	11110111	11111111	11111110	11111100	11111000	11111010	11110101	11111101
PORTB=Temp & i	11110000	11110001	11110010	11110011	11110100	11110100	11110100	11110000	11111000	11110001	11111000




.
.
.

Note:
The & (bitwise AND) operator compares each bit of its first operand to the corresponding bit of the second operand. If both bits are 1's, the corresponding bit of the result is set to 1. Otherwise, it sets the corresponding result bit to 0.

---------------------------

[Acetronics2]

Hi, Ioannis

And what about your I/O "defines" ( TRISB = ??? ) did you declare the input and output pins ???

Or use individual "HIGH" 's .or "LOW" 's..

Just an idea ...

Alain

[sayzer]

I think I found the problem.

Here it is.

1st	i=240		11110000
	PortB		11110000 'an example.
	Temp=PORTB	11110000
	PORTB=Temp & i	11110000
		
2nd	i=241		11110001
	PORTB		11110000
	Temp=PORTB	11110000
	PORTB=Temp & i	11110000
		
3rd	i=242		11110010
	PORTB		11110000
	Temp=PORTB	11110000
	PORTB=Temp & i	11110000
.
..
...
Etc..

The first time you get i=240 in decimal. Which is 11110000.
Then, whatever you "bitwise AND" it with, you will always get 11110000.

Thus, after 240, you will always have 11110000 because each time loop increments, you assign the previous PORTB value to the temp variable.


-------------------

[mister_e]

For i=0 to $0F
    PORTB= i 
next

[Ioannis]

Thanks everyone for the response.

Well sayzer gave me the kick-start!

What I was needed was to keep the upper bits while setting or reseting the lower according to the counter in the for - next loop. This is done first by clearing the lower bits, then OR-ing with the new value. I was too tired to see it immediatly. But, thanks for the try...

The new code should look like this:

for i=240 to 250
temp=portb
temp=temp & $F0
temp=temp|i
portb=temp
pause 1000
next i

Thanks again,

Ioannis

[paul borgmeier]

Steve's does it... but if you do not want to fiddle with the upper nibble latch

For i=0 to $0F
    temp = PORTB & $F0 ' keep upper nibble
    PORTB= temp | i       ' keep upper, set lower to i
next

EDIT - Wow - a lot happens in 10 minutes - I was replying to Steve's #5 and 3 more got in there! :-)
and attachments did not work for me yesterday - I got corrupt error when tried to open