Subject:
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Re: BCD
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Thu, 3 Apr 1997 02:53:32 GMT
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Original-From:
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MAR ERICSON <mar@cooper./antispam/edu>
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Viewed:
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4066 times
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Yeah, it helps alot. Thanks.
I guess the half-cary is for adding to the next significant 4 bit word.
And the current word, including overflow, is then subtracted by ten
(1010), if the half-carry is flaged, to yield the proper BCD word.
Is this what happens? If so, does this create an extra cycle of execution?
-----------
ericson mar
Master of Engineering Candidate
Project: Mobile Robotics
mar@cooper.edu
(212)353-4356
Department of Mechanical Engineering
The Cooper Union for the Advancement of Science and Art
-------------------------------------------------------
On Wed, 2 Apr 1997, Rajesh Gottlieb wrote:
>
> > Does anyone know the details of how a BCD number is stored?
> > I'm unsure as to what a "half-carry" is in HC11 CCR.
> > It would be great if someone can provide a little example. :)
>
> As far as BSD goes; every decimal digit is represented by four binary
> digits:
>
> decimal BCD
> 0 0000
> 1 0001
> 2 0010
> 3 0011
> 4 0100
> 5 0101
> 6 0110
> 7 0111
> 8 1000
> 9 1001
>
> so that a number like 3725 would be represented by
> 0011 0111 0010 0101
>
> I've never heard the term "half-carry" before, but it might be related to
> the fact that you can't add two BCD's as if they were ordinary binary
> numbers. For example if you were to perform to operation 3725 + 6 you
> would get
>
> 0011 0111 0010 0101
> + 0000 0000 0000 0110
> _____________________
> 0011 0111 0011 0001
>
> Hope this helps
>
> Rajesh
>
>
>
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Message has 2 Replies:
 | | Re: BCD
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| Mar, The half carry (H) bit in the CCR sets if there is a carry from bit 3 to bit 4: in other words when there is a carry from the low hex digit to the high hex digit. Only the DAA instruction is affected by the state of H. For example: LDAA #$5A (...) (30 years ago, 3-Apr-97, to lugnet.robotics.handyboard)
| | | hbsonar
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| I am trying to run 4 sonar sensors from the HB, and I'm not sure how to go about doing this. I have a copy of the code from the ftp://cherupakha.med...ntrib/kent directory, but I'm pretty bad with assemby language and I'm not sure what I would need (...) (30 years ago, 19-Apr-97, to lugnet.robotics.handyboard)
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Message is in Reply To:
| | Re: BCD [DAT]
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| (...) As far as BSD goes; every decimal digit is represented by four binary digits: decimal BCD 0 0000 1 0001 2 0010 3 0011 4 0100 5 0101 6 0110 7 0111 8 1000 9 1001 so that a number like 3725 would be represented by 0011 0111 0010 0101 I've never (...) (30 years ago, 2-Apr-97, to lugnet.robotics.handyboard)
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