Why 8255 ppi

RD — It is the signal used for read operation. A low signal at this pin shows that CPU is performing read operation at the ports or status word. Or we can say that is providing data or information to the CPU through data buffer. WR — It shows write operation. A low signal at this pin allows the CPU to perform write operation over the ports or control register of using the data bus buffer.

A 0 and A 1 : These are basically used to select the desired port among all the ports of the and it do so by forming conjunction with RD and WR. It forms connection with the LSB of the address bus. Reset : It is an active high signal that shows the resetting of the PPI. A high signal at this pin clears the control registers and the ports are set in the input mode.

Initializing the ports to input mode is done to prevent circuit breakdown. As in case of reset condition, if the ports are initialized to output mode then there exist chances of destruction of along with the processor. As we can see that pin number 27 to 34 is allotted to data bus. These are tri-state data bus lines of bidirectional nature that connects with the processor.

These are used to allows flow of data and control or status word between the and the processor. The external voltage required to drive the circuit is provided at pin number 26 i. Also pin number 7 is the ground connection of the circuit. Uncommon Carriers John McPhee. The Art of War Sun Tsu. Related Audiobooks Free with a 30 day trial from Scribd.

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Akash Gavture. Show More. Views Total views. Actions Shares. No notes for slide. User can give information i. IN, OUT etc. The ports can be programmed to function either as a input port or as a output port in different operating modes. It requires 4 internal addresses and has one logic LOW chip select pin. Its main functions are to interface peripheral devices to the microprocessor. Next Page.

Dashboard Logout. It is an active low input pin for If this pin is at logic 0, the chip is selected for communication with the microprocessor.

If the chip is not selected the data lines D of will be in tristate. These pins are the data pins, which are used by for communication with the microprocessor. They are connected to the data bus of the microcomputer system. These are address-input pins. They select one of the ports inside for communication with the microprocessor. It is an active high input pin. It is connected to ResetOut output of It is used to reset the After a reset of , all the three ports of work as input ports in mode 0, which is the simplest mode of operation.

Operational modes of Ports are described later.