8255(programmable peripheral interference)
• The 82C55 is a popular interfacing component, that can connect any I/O devices to a microprocessor.
• It is used to connect the keyboard and a parallel printer port in PCs (usually as part of an integrated chipset).
• There are eight bit ports available for interfacing input output on the IC package of 8255 . These three ports may be divided into two groups. There are three modes of operation available. User will select the desired mode according to the requirement.
A1 AO select
0 0 port A
0 1 port B
1 0 port c
1 1 command register
MODES OF OPERATION
There are three modes of operation
1. MODE 0
2. MODE 1
3. MODE 2
MODE 0
In mode 0 all the three ports A, B and c for data input and output independently, there is no handshaking required data can be simply write or can read from specific port…show more content… Mode 0 – input mode
In the input mode, the 8255 receive data from the external ports and also the CPU reads the received data from its data bus.
Mode 0 - output mode
In the output mode, the CPU sends data to 8255 through system data bus and the external peripheral ports receive this data through 8255 ports.
MODE 1
In mode 1 port A and port B can be programmed for strobed data input or buffered data output operations. Port c bits will serve as control signals for facilitating the data transfer ports A and B. Port A and Port B of this mode uses the lines on Port C to transmit or accept “handshaking” signals.
The mode 1 which supports handshaking has following features:
Two ports port A and B can be used as 8-bit input and output ports.
Each port uses three lines of port c as handshake signal and remaining two signals can be used as input and output ports.
Also Input and Output data are
