Bitwise operations and masks: basics, help?

[xnihilo]

Hi,

I know there are the bitwise operators to work at bit level. I'm not familiar with these and logic was never my strong point. That's why I would need some help here.

I'm using a 7 segments led display (plus a dot, which makes 8 leds, and two ground pins, for a total of 10 pins).
Each segment is a led. The 7 sements (plus the dot led) have common cathode.
Each led anode is connected to a pin of a PIC16F684. So to turn on a segment, I just need to output 5V on the appropriate pin. To display a digit, I just have to turn on the appropriate pins/segments/leds.

I'm using RC4 to RC0 for 5 of the 7 segments (segments a to e) and RA1 to RA2 for the 2 last segments (f, g) (while the "dp" dot is on RA0).

I have to set the appropriate pins to display the adequate segments to display a digit.
For example, to display digit "0", I need to turn on the pins that will light the segments a, b, c,d, d, e, f, thus, for my design, the pins RC4 to RC0 and RA1. (a little complicated, yes).
Anyway, I have to set portA and portC to:


porta: xxxx10x, portc: x11111

where the "x" represent bits that must not be changed.

How can I replace the needed bits without changing the "x" bits?

I guess I should use bits mask but what is the magic?

Thanks for any help here.

Regards.

[mister_e]

when you want to clear a bit you use AND, set a bit OR

portc: x11111

PORTC=PORTC | %00011111

<hr>
porta: xxxx10x,

for this one you may also do it simple..
TempVar=PORTA
TempVar.1=0
TempVar.2=1
PORTA=TempVar

OR, in some case, the following will work without much problem
PORTA.1=0
PORTA.2=1

HTH

[xnihilo]

when you want to clear a bit you use AND, set a bit OR

portc: x11111

PORTC=PORTC | %00011111

<hr>
porta: xxxx10x,

for this one you may also do it simple..
TempVar=PORTA
TempVar.1=0
TempVar.2=1
PORTA=TempVar

OR, in some case, the following will work without much problem
PORTA.1=0
PORTA.2=1

HTH

Hello,

Simple?
Not so simple because each digit on the 7segments display needs (in my design) a pair of bytes for porta and portc that are found in a 10 entries array, and I prefer not to use intermediate variable.
Sorry but I didn't understand your example above:

portc: x11111
PORTC=PORTC | %00011111
porta: xxxx10x,



let's say porta value is %00011001 and I need to alter only bits 1 and 2 with the following pattern stored in a BYTE varible called "avar":
variable avar value is %-----10-

???

Can I isolate a chunk of a byte and insert it at a desired position in anoter byte?

[mister_e]

Yes i see some different ways, just paste your pattern here and where to send them, i'll give you something to think about.

[xnihilo]

Example:

The bits I need to set to display the "0" digit on the 7 segments display are:

on porta: %***01* , all other bits are left untouched
on portc: %*11111 , bit 5 is left untouched.

I have two arrays of bytes:
cval VAR BYTE[10] and aval VAR BYTE[10], each index represents a duet of bytes containing the bits configuration to display a digit.
arrays index 0 for digit "0",... up to digit "9" in index 9.

I only need to 'insert' chunks of bits in porta and portc registers.


For a given array index (representing the 7 bits to make a digit):
For porta I will need to replace bits 1 and 2 from porta by bits 1 and 2 from aval variable.
For portc I will need to replace bits 4 to 0 from portc by bits 4 to 0 from cval variable

is this clear ???

[mister_e]

Why not a WORD array instead? Anyways, yes it's clear enough. I'll do something a little bit later.