May 2024
Intermediate to advanced
889 pages
30h 8m
English
book
The X 86 Microprocessors: Architecture, Programming and Interfacing (8086 to Pentium) 2nd Edition by Pearson
by Lyla B. Das
Content preview from The X 86 Microprocessors: Architecture, Programming and Interfacing (8086 to Pentium) 2nd Edition by Pearson
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19-32
THE
x86 MICROPROCESSORS
Then the MSBs are added. There are five numbers to be added, the fifth being the
sum of the ‘carry’ of LSB addition. This is in address 49H and the pointer R1 points to
this as the last operand.
We have used numbers which do not generate carries in the MSB addition. The sum is
limited to four hex digits. The sum is finally in R4 and R5, with R4 = 0A7H and R5 = 4EH.
19.9.4.2
|
Subtraction Instructions
SUBB A, src
This subtracts the source byte and the carry flag from A and puts the result in A. The OV,
CY and AC flags are affected. This is actually a ‘subtract with borrow’ instruction. There
is no subtraction instruction, as such. For subtraction, the carry flag is cleared and then
the operation is done.
An example of a typical ...
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