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Code question for driving a 7447 BCD to 7 Segment TTL IC

 
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Tom-H-PIC



Joined: 08 Sep 2003
Posts: 105
Location: New Castle, DE

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Code question for driving a 7447 BCD to 7 Segment TTL IC
PostPosted: Mon Nov 28, 2011 7:23 am     Reply with quote
I have a 7447 BCD to 7 Segment driver IC connected to port b bits 0-3.
I'm using this with a 8 digit VDF tube to multiplexing a through g.
I'm look for the most speed that I can get.
Right now I'm using a modified send nibble fiction from the LCD programs.
But this seems to be slow.

What is the easiest way of send a nibble to a port without affecting the 4 MSBs?
Is there a faster way just to change the lower 4 bits of a port?

Thank You All in advance!
Tom
asmboy



Joined: 20 Nov 2007
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PostPosted: Mon Nov 28, 2011 10:57 am     Reply with quote
Code:

byte newnib; // focus=low 4 bits  - you can use SWAP(newnib) twice if its HIGH
// get the current value and do some masking
output_B((input_b()&0xF0)|(newnib&0x0F));


this MAY take up to 12 instructions to accomplish on a 16F886
but due to better memory access never needs more than 8 clocks
on an 18F4520

( to use fewer clocks where memory is in play -
always consider the 18F parts )

U can see if this works for you well enough.
meanwhile....
i can't wait to see how the REALLY clever folks on the forum would do this,
as i am always eager to learn how to use fewer clock cycles myself.
Very Happy
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