The 8085 microprocessor was introduced by Intel in 1976. It is a better or upgraded version of the 8080 microprocessor. The 8085 microprocessor has a set of registers that are used to store data and addresses. The most important registers are the accumulator (A), the program counter (PC), the stack pointer (SP), and the flags register. The accumulator is used to perform arithmetic and logical operations, and the program counter is used to store the address of the next instruction to be executed. The stack pointer is used to manage the stack, and the flags register stores various flags that indicate the status of the microprocessor after an operation. In this section, we will discuss the Pin diagram of the 8085 microprocessor
8085 Microprocessor Pin Diagram
The Pin diagram of the 8085 microprocessor has 40 pins that are classified into seven groups: address bus, data bus, control signals and status signals, power supply, and frequency, Reset signals, DMA signals, and serial input/output ports.
1) Address Bus and Data Bus
The address bus contains sixteen lines, numbered A0-A15. The address bus is unidirectional, which implies that bits flow in only one direction from the microprocessor unit to the peripheral devices, and it utilizes the high-order address bus.
2) Control and Status Signals
These signals are used to determine the type of operation being performed. There are three control and three status signals.
RD, WR, and ALE are the three control signals.
RD indicates that the selected IO or memory device is to be read and is ready to accept data from the data bus.
WR This signal indicates that the data on the data bus is about to be written into a specific memory or IO location.
ALE is a positive going pulse generated by the microprocessor when a new operation is initiated. When the pulse becomes high, it denotes the address. When the pulse falls, it indicates that data has been received.
3) Power Supply and Clock Frequency
These are 2 power supply:
Vcc Power supply +5v
Vss Ground Reference
There are 3 clocks signal
XI, X2 – These two pins are connected to a crystal. Because the frequency is internally divided by two, a system operating at 3MHZ requires a crystal with a frequency of 6MHZ.
CLK (OUT) – This signal can be used by other devices as the system clock.
4) Interrupts and Peripheral Initiated Signals
The 8085 has five interrupt signals that can be used to stop the execution of a program.
INTR I (ii) RST 7.5 (iii) RST 6.5 (iv) RST 5.5 (v) TRAP
The INTA signal is used by the microprocessor to acknowledge Interrupt Request. There are three externally initiated signals in addition to Interrupts: RESET, HOLD, and READY. It has one signal called HLDA that responds to HOLD requests.
INTR stands for interrupt request.
INTA’ – A microprocessor interrupt acknowledgment sent after INTR is received.
5) Reset Signals
RESET IN -When the signal on this pin is low(0), the program counter is reset, the buses are tri-stated, and the microprocessor unit is reset.
RESET OUT – Indicates that the MPU is being reset. Other devices can be reset using the signal.
6) DMA Signals
HOLD – This indicates that another device wants to use the address and data bus. When a HOLD request is received, the microprocessor relinquishes the use of the buses as soon as the current machine cycle is completed. Internal processing may be resumed. The processor regains bus access after the HOLD signal is removed.
HLDA – This is a signal that indicates that a HOLD request has been received. When a HOLD request is removed, the HLDA goes low.
7) Serial I/O Ports:
There are two serial signals, SID and SOD, that are used for serial communication.
SOD (Serial output data line) The SIM instruction sets/resets the output SOD.
SID (Serial input data line): When a RIM instruction is executed, the data on this line is loaded into the accumulator.
These pins are used to connect the 8085 microprocessor to other components in a computer system, such as memory, input/output devices, and other microprocessors. Each pin serves a specific function, such as providing power to the processor, transferring data to and from memory and input/output devices, and controlling the operation of the processor.
Frequently Asked Questions(FAQs)
Here are the FAQs on the Pin diagram of 8085 microprocessor.
Q1: What is the purpose of the address bus in the 8085 microprocessor?
A: The address bus is used to transfer memory addresses to the memory or input/output devices. The address bus consists of 16 lines in the 8085 microprocessor, which allows it to access up to 64KB of memory.
Q2: What is the purpose of the data bus in the 8085 microprocessor?
A: The data bus is used to transfer data between the microprocessor and memory or input/output devices. The data bus consists of 8 lines in the 8085 microprocessor, which allows it to transfer 8 bits of data at a time.
Q3: What is the purpose of the control signals in the 8085 microprocessor?
A: The control signals are used to control the timing and sequencing of operations in the microprocessor. These signals include Read/Write (R/W), Clock (CLK), Interrupt Request (INTR), and Reset (RESET), among others.
Q4: What is the purpose of the status signals in the 8085 microprocessor?
A: The status signals are used to indicate the status of the microprocessor during different phases of its operation. These signals include S0 and S1, which provide information about the current machine cycle.
Q5: What is the purpose of the Interrupt Request (INTR) pin in the 8085 microprocessor?
A: The Interrupt Request (INTR) pin is used to request the microprocessor to stop its current operation and service an interrupt request from an external device.
Q6: What is the purpose of the Ready (READY) pin in the 8085 microprocessor?
A: The Ready (READY) pin is used to synchronize the operation of the microprocessor with the external memory or input/output devices.