Draw and explain interfacing of 8086 with 8255 I/O mapped I/O mode.

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meghalikalyankar • 2.3k

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8255 is a programmable peripheral interface. It is used to interface microprocessor with I/O devices via three ports: PA, PB and PC.
All ports are 8-bit and bidirectional. 8255 transfers data with the microprocessor through its 8-bit data bus. The two address lines A1 and A0 are used to make internal selection in 8255.
D7-D0 is connected to data lines of 8086, (RD) ̅ and (WR) ̅ is connected to (IOR) ̅ and (IOW) ̅.
A1 and A0 are connected with A2 and A1 of 8086 processor and A0 of 8086 is used bank selection along with BHE.
They can have 4 options, selecting PA, PB, PC or the control word. The ports are selected to transfer data. The Control word is selected to send commands. Two commands can be sent to 8255, called the I/O command and the BSR command.
I/O command is used to initialize the mode and direction of the ports.
BSR command is used to set or reset a single line of Port C.

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