When the PS(active low)/EN(active low) pin of 8259A used in buffered mode, then it can be used as a

Quiz questions on programmable interrupt controllers like 8254, 8259A, 8251 and keyboard controller 8279. A programmable peripheral interface (PPI) is a multiport device that can be used to connect peripheral devices to a processor's data bus. The PPI 8255 is a general purpose PPI that can be used with almost any microprocessor, and is designed to interface the CPU with its outside world. It has three 8-bit bidirectional I/O ports, A, B, and C, that can be programmed in different modes. The 8255 also has a control register that defines each port's function and mode of operation.  The 8255... Show more

Quiz questions on programmable interrupt controllers like 8254, 8259A, 8251 and keyboard controller 8279.

A programmable peripheral interface (PPI) is a multiport device that can be used to connect peripheral devices to a processor's data bus. The PPI 8255 is a general purpose PPI that can be used with almost any microprocessor, and is designed to interface the CPU with its outside world. It has three 8-bit bidirectional I/O ports, A, B, and C, that can be programmed in different modes. The 8255 also has a control register that defines each port's function and mode of operation. 

The 8255 has the following operating modes:
Bit set reset (BSR) mode: In this mode, only port C bits are used for set or reset.
Input-Output mode: This mode is further divided into three modes. 
The 8255 can be used to transfer data under various conditions, from simple input-output to interrupt input-output. It's economical, functional, and flexible, but it is also a little complex. 

Here's how the 8255 interfaces with special purpose programmable peripheral devices:
When an output device wants to receive data, it checks if the output buffer full (OBF*) signal is 0.
If 0, it receives data on PB7-0 and activatesAcknowledge (ACK*) signal.
When ACK* goes high, the data goes out of the port and OBF* is set to 1.
If the Port interrupt is enabled, INT is activated. 

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