8255 PCI modes of operation Mode 0 1 and 2

They have two mode of operaton
1)Bit Set /Reset mode and
2)Input / Output mode

1)Bit Set /Reset mode:
   In this mode the  individual bit of the port c can be set or reset using the control word.
To learn about control word ,search " control word " in our search box.

2)Input / Output mode :
In this mode it operates in three mode
   a) Mode 0
   b) Mode 1
   c) Mode 2

   a) Mode 0:
          In this mode 8255 is used as simple /input output mode.If port A and B are initialised as mode 0 then port C can be used as i) a 8-bit port                   
                                              ii)two 4 bit ports c
The two halves of the Port C works independently

b)Mode 1:

•   In this mode 8255 is used handshaking output mode.
• Ports A and B function as 8-bit I/O ports and use bits from port C ass handshaking signal.
• If  port B mode 1 input PC0 , PC1, PC2 handshaking signal 
• If port A mode 1 input PC3 , PC4 ,PC5 and If port A mode 1 output PC3,PC6,PC7 
•  handshake  and PC4 and PC5 general input output

c) mode 2

• Bidirectional handshake
• Only port A can be initialized as a bidirectional Handshake
• 5 pins (PC3 - PC7 ) are used for control and status of 8-bit bidirectional bus
• If Port A Mode 2 PC3 - PC7 handshaking lines
• PC0 - PC2 GEneral input output if port b is in Mode 0