NVIS 5586A, Learning Material

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Nvis 5586A
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Accumulator register consists of two 8-bit registers AL and AH, which can be combined
together and used as a 16- bit register AX. AL in this case contains the low-order byte of the
word, and AH contains the high-order byte. Accumulator can be used for I/O operations and
string manipulation.
Base register consists of two 8-bit registers BL and BH, which can be combined together and
used as a 16-bit register BX. BL in this case contains the low-order byte of the word, and BH
contains the high-order byte. BX register usually contains a data pointer used for based,
based indexed or register indirect addressing.
Count register consists of two 8-bit registers CL and CH, which can be combined together
and used as a 16-bit register CX. When combined, CL register contains the low-order byte of
the word, and CH contains the high-order byte. Count register can be used in Loop,
shift/rotate instructions and as a counter in string manipulation.
Data register consists of two 8-bit registers DL and DH, which can be combined together and
used as a 16-bitregister DX. When combined, DL register contains the low-order byte of the
word, and DH contains the high order byte. Data register can be used as a port number in I/O
operations. In integer 32-bit multiply and divide instruction the DX register contains high-
order word of the initial or resulting number.
The following registers are both general and index registers:
Stack Pointer (SP) is a 16-bit register pointing to program stack.
Base Pointer (BP) is a 16-bit register pointing to data in stack segment. BP register is
usually used for based, based indexed or register indirect addressing.
Source Index (SI) is a 16-bit register. SI is used for indexed, based indexed and register
indirect addressing, as well as a source data address in string manipulation instructions.
Destination Index (DI) is a 16-bit register. DI is used for indexed, based indexed and
register indirect addressing, as well as a destination data address in string manipulation
instructions.
Other registers:
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Instruction Pointer (IP) is a 16-bit register.
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Flags are a 16-bit register containing 9 one bit flags.