8085 Microprocessor Architecture
It is an 8 bit register which stores the results of arithmetical and logical operations. It is also used to receive data from input port to microprocessor and to send data to output port from microprocessor. It is referred as register A in the program.
2. General Purpose Registers
Registers B, C, D, E, H and L are 8 bit general purpose registers. These registers store 8 bit data temporarily for processing. BC, DE and HL are used as register pairs to store 16 bit data.
3. Flag Register (F)
Flag register is also an 8 bit register which indicate status of the accumulator after any arithmetical or logical operation. Out of 8 bits, five are defined as flags. These flags are given below.
Sign Flag (S) – It indicates the sign of the number. If the number is negative then sign flag is set (changed to 1) and if positive then reset (changed to 0).
Zero Flag (Z) – If after any arithmetical or logical operation, all the bits in accumulator are zero then zero flag is set otherwise reset.
Auxiliary Carry Flag (AC) – If carry is generated from D3 to D4 in the accumulator after any operation then auxiliary carry flag is set otherwise reset. This flag is used internally by microprocessor for BCD operations and cannot be used by the programmer.
Parity Flag (P) – If after any arithmetical or logical operation number of 1’s in accumulator are even, then parity flag is set, otherwise reset.
Carry Flag (CY) – The size of accumulator is 8 bit. If after any operation 9th bit is generated then carry flag is set, otherwise reset.
5. Stack Pointer (SP)
It is a 16 bit register which contains the memory address of top of the stack. Stack is a part of memory which is used to store data temporarily, especially while the execution of subroutines or functions.
The address bus is the group of 16 lines. It is used to carry the address of memory location and address of input and output ports. It is a unidirectional bus, that means the bits can flow only in one direction i.e., microprocessor to the peripherals. The address lines are identified by A15-A0.
2. Data Bus
The data bus is the group of 8 lines which is used to carry data. These lines are bidirectional. These data lines are identified by D7-D0.
3. Control Bus
The control bus comprises of various single lines that carry various control signals for synchronizing various devices and performing different task. The microprocessor generates specific control signals for different operations.
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