8255

Function

The control signal chip select${\displaystyle {\neg }}$CS (pin 6) is used to enable the 8255 chip. It is an active-low signal, i.e., when ${\displaystyle {\neg }}$CS = 0, the 8255 is enabled. The RESET input (pin 35) is connected to the RESET line of system like 8085, 8086, etc., so that when the system is reset, all the ports are initialized as input lines. This is done to prevent 8255 and/or any peripheral connected to it from being destroyed due to mismatch of port direction settings. As an example, consider an input device connected to 8255 at port A. If from the previous operation, port A is initialized as an output port and if 8255 is not reset before using the current configuration, then there is a possibility of damage of either the input device connected or 8255 or both, since both 8255 and the device connected will be sending out data.