8bit Register Containing I/O bits from different PORTS( cutom port)

M

Mehmood Ahmed

New Member

• Nov 30, 2011

• #1

Hi All,

I want to pack I/O bits from different ports into one 8bit variable making it easy for putting data on those pins simultaneously is there possibility. The compiler I am using is hitech C. I want to pack( RB2...RB7 , RC2 , RC3) into one 8bit register or variable so that I can use it as an 8bit data port.

Regards

 

Last edited: Nov 30, 2011

Ian Rogers

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• Nov 30, 2011

• #2

For output..
PORTB = (data << 2) & 0xFC;
PORTC = (data >> 6) & 0x0C;

You may have to OR the ports if they are used for something else

Input
data = ( PORTB >> 2 ) & 0x3F;
data += (PORTC << 6 ) & 0xC0;

 

M

Mehmood Ahmed

New Member

• Dec 1, 2011

• #3

thanks for your reply...my requirement is not this rather I want someway like struct or union or something else that may help me pack those I/O bits into one single register...I want to avoid this method you have just told...please guide me if that is possible the method I want

Regards

 

Ian Rogers

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• Dec 1, 2011

• #4

You are still going to have to shift.. even using a union.. If you set up an integer and a bit-field in a union, you still need to get the bits into the right order. What kind of interface are you doing?

 

Nigel Goodwin

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Most Helpful Member

• Dec 1, 2011

• #5

I think imaging structures and unions is only confusing him, all he needs to do is write a function/procedure to do what he wants.

Something like (not in C):

PortWrite = VariableA

VariableB = PortRead

Trivial to do, and easy to use.

 

Last edited: Dec 1, 2011

Ian Rogers

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• Dec 1, 2011

• #6

Nigel ! I agree the way I proposed IS the best way.. I think union's will over complicate things

 

Nigel Goodwin

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• Dec 1, 2011

• #7

Ian Rogers said:

Nigel ! I agree the way I proposed IS the best way.. I think union's will over complicate things

Click to expand...

Would they even work?, I'm not a C 'person'.

 

Ian Rogers

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• Dec 1, 2011

• #8

The union is a great tool... you can declare an integer (16 bits) and two bytes ( 8 obviously ) and 16 bit_fields.. in one variable .. Very useful for serialization.. The integer and two byte array occupy the same ram space... Quite easily obtained in asm as well.

 

Nigel Goodwin

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• Dec 1, 2011

• #9

Ian Rogers said:

The union is a great tool... you can declare an integer (16 bits) and two bytes ( 8 obviously ) and 16 bit_fields.. in one variable .. Very useful for serialization.. The integer and two byte array occupy the same ram space... Quite easily obtained in asm as well.

Click to expand...

And would that allow you to access bits in different ports?.

 

Ian Rogers

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• Dec 1, 2011

• #10

No... That's why it wouldn't be useful here. I don't think SFR's can be accessed this way in C ( someone may prove me wrong )

 

duffy

Well-Known Member

• Dec 1, 2011

• #11

Ahmed - why do you want to avoid rotate, mask and inclusive-or? From your description (RB2...RB7, RC2 , RC3) I don't think there's any way around it.

Also, you seem to have 1 too many bits there.

 

Last edited: Dec 1, 2011

M

Mehmood Ahmed

New Member

• Dec 1, 2011

• #12

Thanks to both of you seniors.Both of you gave great attention to my problem. On the basis of arguments both of you have given
(also 3v0 said the same thing yesterday when I was on chat) conclusion comes out to be the solution Ian has given and, I am going to use that one. Thank you.
Regards