gnusim8085-devel team mailing list archive

[felixcpfung <felixcpfung@xxxxxxxxx>]

Thank you for your explaination on the behavior of DAA. Please note that in
BCD addition,
74 + 88 = 162. That means after addition and DAA, the accumulator should
hold 62 and carry flag should be 1 and that is the correct behavior.
Otherwise, 100 is missed and you can never make a correct multi-byte BCD
Addition.

Besides, as I reported seperately, 99+1 after DAA, the accumulator holds A0
and carry flag
is 0 which is also wrong.

Based on the above observation, I believe that there must be a bug exist
when doing DAA
conversion.

Perhaps you should run the hardware and also theck the CPU manual for the
real behavior
of the CPU
Regards, Felix


2010/5/26 Onkar Shinde <onkarshinde@xxxxxxxxx>

> Here is the description of DAA instruction I found in -
> http://www.cs.otago.ac.nz/cosc243/lectures/is_detail.pdf
> ****************
> The contents of the accumulator are changed from a binary value to two
> 4-bit binary coded decimal (BCD) digits. This is the only instruction that
> uses the auxiliary flag to perform the binary to BCD conversion, and the
> conversion procedure is described below. S, Z, AC, P, CY flags are altered
> to reflect the results of the operation.
> If the value of the low-order 4-bits in the accumulator is greater than 9
> or if AC flag is set, the instruction adds 6 to the low-order four bits.
> If the value of the high-order 4-bits in the accumulator is greater than 9
> or if the Carry flag is set, the instruction adds 6 to the high-order four
> bits.
> ****************
>
> If you run the program in bug description in debug mode, you will find
> that instruction 'adi 088h' is setting both C and AC flags. Hence when
> DAA is executed 6 is added to both high-order and low-order bits and
> both flags are altered, making then 0.
>
> So as per my understanding the behavior is correct here.
>
> --
> 78+88 in BCD addition missed carry
> https://bugs.launchpad.net/bugs/584093
> You received this bug notification because you are a direct subscriber
> of the bug.
>
> Status in gnusim8085: Triaged
>
> Bug description:
> With the following program, the carry flag is missed:
>
> mvi a,078h
> adi 088h
> daa
> hlt
>
> please check
>
> regards, Felix Fung
>
> To unsubscribe from this bug, go to:
> https://bugs.launchpad.net/gnusim8085/+bug/584093/+subscribe
>

-- 
78+88 in BCD addition missed carry
https://bugs.launchpad.net/bugs/584093
You received this bug notification because you are a member of
GNUSim8085 developers, which is subscribed to gnusim8085.

Status in gnusim8085: Triaged

Bug description:
With the following program, the carry flag is missed:

mvi a,078h
adi 088h
daa
hlt

please check

regards, Felix Fung