Functional Block Diagram of Intel 8085
The functional block diagram of the Intel 8085 microprocessor illustrates the major functional components and their interconnections.
•The main blocks include the ALU (Arithmetic Logic Unit), registers, control and timing unit, interrupt control, and address/data buses.
Here’s a simplified functional block diagram:
8085 Microprocessor Functional Units are:
‣Accumulator in 8085 Microprocessor:
• This is the first unit in the Block Diagram of 8085 Microprocessor. It is an 8-bit register that is used for performing various operations like arithmetic, logical, I/O & LOAD/STORE operations.
•It is connected to the internal ALU and data bus.
‣ Arithmetic and logic unit in 8085 Microprocessor:
• This is the second unit in the Block Diagram of 8085 Microprocessor.
• As the name itself suggests, it is used to perform arithmetic and logical operations on the data like Addition, Subtraction, AND, OR, etc. on 8-bit data.
‣ General-purpose register in 8085 Microprocessor:
• This is the third unit in the Block Diagram of 8085 Microprocessor.
• There are 6 general-purpose registers that are present in the 8085 processor, i.e. B, C, D, E, H & L. Each register can hold 8-bit data.
• These registers can operate to hold 16-bit data in pairs and their pairing combinations are like B-C, D-E, and H-L.
‣ Program counter in 8085 Microprocessor:
This is the 4th unit in the Block Diagram of 8085 Microprocessor.
• It is a 16-bit register that is used for storing the memory address location of the next instruction to be executed.
• The microprocessor increments the program whenever an instruction is being executed so that the program counterpoints to the memory address of the next instruction that is going to be executed.
‣ Temporary register in 8085 Microprocessor:
• This is the 6th unit in the Block Diagram of 8085 Microprocessor.
• It is an 8-bit register, that is used to hold the temporary data of operations performed like arithmetic and logical operations.
•‣ Flag Register in 8085 Microprocessor:
• This is the 7th unit in the Block Diagram of 8085 Microprocessor.
• It is an 8-bit register consisting of five 1-bit flip-flops, that can hold either 0 or 1 depending upon the result that is stored in the accumulator.
• These are the set of 5 flip-flops:
- Sign (S)
- Zero (Z)
- Auxiliary Carry (AC)
- Parity (P)
- Carry (C)
‣ Instruction register and decoder in 8085 Microprocessor:
• This is the 8th unit in the Block Diagram of 8085 Microprocessor.
• The instruction register and decoder are 8-bit registers. At the very moment when an instruction is fetched from memory, it is stored in the Instruction register.
• The instruction decoder is responsible for decoding the information present in the Instruction register.
‣ Timing and control unit in 8085 Microprocessor:
• This is the 9th unit in the Block Diagram of 8085 Microprocessor.
• It provides timing and control signals for the microprocessor to operate.
• These are the timing and control signals, which control various external and internal circuits.
‣ Interrupt control in 8085 Microprocessor:
• This is the 10th unit in the Block Diagram of 8085 Microprocessor.
• The interrupt control controls the interrupts during a process.
• During the execution of the main program, whenever an interrupt occurs, the control is shifted from the main program to process the incoming request.
• After the completion of the request, the control again goes back to the main program.
‣ Serial Input/output control:
• This is the 11th unit in the Block Diagram of 8085 Microprocessor.
• It is responsible for controlling the serial data communication by using two instructions: SID (Serial input data) and SOD (Serial output data).
‣ Address buffer and address-data buffer:
• This is the 12th unit in the Block Diagram of 8085 Microprocessor
. • The content that is stored in the stack pointer and program counter is loaded into the address buffer and address-data buffer for communicating with the CPU.
•These buses are connected to the memory and input/output chips; the CPU can exchange the desired data with the memory and input/output chips.
•‣ Address bus and data bus:
• This is the 13th unit in the Block Diagram of 8085 Microprocessor.
• The data bus only carries the data that is to be stored.
• It is bidirectional, whereas the address bus carries the location to where it should be stored and it is unidirectional.
• It is also used for transferring data & Address I/O devices.
Pin Configuration:
‣ VCC (+5V):
Power supply pin. Connects to a +5V DC power source.
‣ GND (Ground):
Ground reference pin.
‣ CLK (Clock):
Input for the clock signal. The microprocessor synchronizes its operations with this clock.
‣ SID (Serial Input Data):
Serial input data line for serial communication.
‣ SOD (Serial Output Data):
Serial output data line for serial communication.
‣ RST7.5, RST6.5, RST5.5, RST4.5, RST3.5, RST2.5, RST1.5, RST0.5:
Restart interrupt inputs. These pins are used to provide restart operations for specific interrupt conditions.
‣ INTR (Interrupt Request):
Interrupt request input. External devices can request an interrupt using this pin.
‣ INTA (Interrupt Acknowledge):
Interrupt acknowledge output. Indicates that the microprocessor has recognized an interrupt request.
‣ RESET:
Reset input. When a high signal is applied to this pin, the microprocessor is reset.
‣ X1 and X2:
External oscillator connections. Connect an external crystal or oscillator circuit for generating the clock signal.
‣ S7, S6, S5, S4, S3, S2, S1, S0 (Status Pins):
Status output pins indicating the status of various operations during machine cycles.
‣ ALE (Address Latch Enable):
Output signal used to latch the lower order address bits onto the external address bus during the first clock cycle.
‣ AD0-AD7 (Address/Data Bus):
Multiplexed bidirectional lines for transmitting both address and data.
‣ A8-A15 (Higher Order Address Bus):
Unidirectional lines for transmitting higher-order address bits.
‣ IO/M (Input/Output and Memory):
Output signal indicating whether a memory or I/O operation is being performed.
‣ HLDA (Hold Acknowledge):
Hold acknowledge output signal for DMA (Direct Memory Access) operations.
‣ HOLD:
Hold input. Used to request the microprocessor to release control of the address and data buses.
‣ READY:
Input signal indicating whether the microprocessor is ready to accept the next instruction.
‣ MREQ (Memory Request):
Output signal indicating a memory read or write operation.
‣ IORQ (Input/Output Request):
Output signal indicating an I/O read or write operation.
‣ RD (Read):
Output signal indicating a read operation.
‣ WR (Write):
Output signal indicating a write operation.
‣ Status Pins (S1, S0):
Status output pins indicating the status of various operations during machine cycles.
‣ ALE (Address Latch Enable):
Address latch enable output signal for latching the lower order address bits onto the external address bus during the first clock cycle.
