Changes
8255
,[[File:Intel 8255A - IO modes control word format.jpg]]
== Group Modes ==
=== Mode 0 – Simple Input/output mode ===
In this mode the 8 bit port A (PA0-PA7) of 8255 IC can be configured as input or output port. In the similar fashion port B (PB0-PB7) can also configured as input or output operation. However there is flexibility for the port C. It can be divided into two 4 bit ports, the port CLower (PC0-PC3) and port CUpper (PC4-PC7). Each of them can set independently for input or output operation. In this way we can say there are four ports (port-A, port-B, port CLower and port CUpper) and each of them can set either as an input port or an output port.
Here these ports are simple input or output ports. That means these ports can work without handshaking. In this mode the outputs are latched whereas the inputs are not latched.
[[File:8255 - mode-0.png]]
=== Mode 1 – Strobed Input/output or Handshake mode ===
Mode 1 is a second mode of 8255 I/O mode. In this mode of operation handshaking can used for the input or output data transfer. Another important think we have to remember that there are two groups in 8255 PPI, Group A and Group B. Both these groups have one 8-bit port and one 4-bit port.Group A consist Port-A and Port CUpper. And group B consist Port-B and Port CLower. The 8-bit port of each group can be programmed for input or output operation with latched input and latched output facilities. The bits of Port C used for handshaking.
[[File:8255 - mode-1.png]]
=== Mode 2 – Bidirectional Mode ===
So the final mode of 8255 is Mode 2. In this mode Port A can be programmed to operate as a bidirectional port. When Port A programmed in this mode of operation, Port B can used either in Mode 0 or Mode 1. For mode 2 operation PC3 to PC7 bits used for handshaking. In this mode too both inputs and outputs are latched.
[[File:8255 - mode-2.png]]
== Programming Examples ==
