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Re: [f-cpu] manual 0.27c
On Wed, Dec 04, 2002 at 11:24:08AM +0100, Karl-Heinz Eischer wrote:
> the manual states on page 88 (instruction sub):
>
> The borrow flag (same as carry) indicates that the borrow value is written
> to register number (r1^1). If no borrow has been generated, the neighbour
> register is cleared, otherwise the neighbour register is set to 1.
>
> The examples show that it is set to 0xFF. Furthermore there is the order
> inconsitent is the description. First it states r2 - r3 and a few lines
> later (r3 - r2). The example shows r2 - r3.
When I implemented EU_ASU, I noticed that it's much simpler to set the
borrow register to `1' instead of `-1' (all ones). It also matches the
carry output of the addc operation, and is more logical: we borrow 1,
not -1 (borrowing -1 means adding 1). That is, the example is wrong.
--
Michael "Tired" Riepe <Michael.Riepe@stud.uni-hannover.de>
"All I wanna do is have a little fun before I die"
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