Registers – are a type of computer memory used to quickly accept store and transfer data and instructions that are
being used immediately by the CPU.
Segment Register – holds the addresses of instructions and data in memory which are used by the processor
access memory locations.
AX & Dx - ?????
BX – instructions where we need to specify in a general purpose register the 16 bit effective address of a memory
location.
CX – is always used in loop instructions, it is always the implied counter.
Flags – are modified kind of register that record the condition of a microprocessor’s calculation.
Status flag – reflect the result of executing an instruction. Cannot be set directly. (There are 6 SF)
Control flag – enable or disable Certain CPU operations. (There are 3 control Flags)
Sequential Logic Circuit – have a inherent memory built in
Event driven – Asynchronized circuit that changes immediately when available.
Clock Driven – Synchronized to clock signal.
Pulse Driven – Responds to trigger pulses.
SR FLIP FLOP – a one bity memory bistable device that has two inputs S for set and R for reset or 1 or 0.
A flag is set if its 1.
Directional Flag – affects the direction of moving data blocks by such instructions as MOVS CMPS and SCAS
Interrupt Flag – Dictates whether system interrupts can occur.
Interrupts – are actions initiated by hardware block such as input devices that will interrupt normal
execution of programs.
Trap Flag – determines whether the CPU is halted after the execution of each instruction.
Carry Flag – is set when the result of an unsigned arithmetic operation is too large to fit in the destination register.
Overflow Flag – determines whether the arithmetic operation is too large to fit in the destination register.
Overflow can occur when adding two numbers with the same sign.
Sign Flag – is set when the sign of arithmetic or logic operation is negative.
Zero Flag – is set when the result is equal to zero. A value of 1 means the result is 0 a value of zero means its value
is not 0
Auxiliary carry Flag - is set when an operation causes a carry from bit 3 to bit 4 ( or a borrow from bit 4 to bit 3 ) of
an operand. A value of 1 = carry a value of 0 = no carry
Parity Flag – reflects the number of 1s in the result of an operation.