In this course, we will study the pin diagram of 8085 microprocessor and its description.
The 8085 pin diagram consists of 40 pins of the microprocessor. The pins can be categorized into six groups-address and data bus, control signals, status signals, power supply, and serial input/output ports.
The x1 and x2 represent the crystal oscillator which will provide frequency for the microprocessor.
The address bus pins range from A8 to A15 and these pins do the data transfer only.
The address bus pins or data bus pins range from AD0 to AD7, and these pins are called multiplexing lines that can do both addresses as well as data transfer.
It is an active high signal. It represents the status of data lines (AD0-AD7). If the value is positive than it indicates that the address is going in the lines and if the value is negative than data is traveling in the lines.
It tells us whether the address is intended for memory or input/output. In the case when we get a positive signal it represents that we have got i/o read or i/o write and when we get a negative signal it represents memory activation.
The status signals S0, S1 gives different functions as well as status based on their status.
The RD is an energetic low signal and it is used for controlling the microprocessor READ operation. When the RD pin goes small then the 8085 microprocessor understands the information from the I/O device or memory.
It has the power to control the microprocessor’s write operations. When the WR pin goes small the data will be written to the I/O device or memory.
The READY pin is for ensuring whether a device is set for accepting or transferring data. When the pin is high the device is ready for transfer, if it is not then the microprocessor stays until this pin goes high.
The HOLD pin specifies when any device is demanding the use of address as well as a data bus.
It is the response signal of HOLD and is used to specify whether this signal is obtained or not. This signal will go low after the implementation of HOLD demand.
This is an interrupt signal, and the priority of this among the interrupts is low. This signal can be allowed or not allowed by the software. The 8085 microprocessor completes the instruction which is being executed when the INTR pin goes high and recognizes the INTR signal and progresses it.
INTA stands for interrupt acknowledgment. Whenever an interrupt signal comes, then it should be recognized by INTA. It is an active-low signal that is for zero it will process and for one it won’t.
These are the restart maskable interrupts or Vectored Interrupts which is used for insertion of an inner restart function repeatedly. All these interrupts are maskable.
TRAP is a non-maskable interrupt, and it doesn’t allow or stop a program. TRAP has the maximum precedence between the interrupts. The priority order is TRAP, RST 5.5, RST 6.5, RST 7.5, and INTR.
It is used to reset the program counter toward zero. It also rearranges interrupt enable as well as HLDA flip-flops (FFs).
It will reset all the devices connected to the microprocessor.
X1, X2 terminals that are associated with the exterior oscillator for generating the required as well as appropriate operation of a clock.
Sometimes CLK signal has to be generated from microprocessors that can be used in favor of other peripherals or else other digital integrated circuits. This is offered with a CLK pin.
These two pins are used for serial data communication. In the serial input data, the information is uploaded into the 7th-bit of the accumulator while RIM instruction is performed. RIM(Read interrupt mask) verifies whether the interrupt is covered or not covered. In the serial o/p data the output of the data is sent toward the 7th-bit of the accumulator whenever an instruction of SIM is performed.
VSS is a ground pin whereas Vcc is a +5v pin.