Is a drain switch Type bi-direction

Is a drain switch Type bi-directional I / O interface, commonly known as the data bus interface. Only the P 0 port can read and write directly to the external memory. It can be used as a general-purpose input / output port and can drive eight TTL logic levels per bit. The PIN is used as a high impedance input when writing "1" to the P 0 port. The P0 port is also used as a low 8 bit address / Data multiplexer when accessing external programs and data storage. In this mode, p 0 has an internal pull up resistance. In flash programming, the P0 port is also used to receive instruction bytes; in Program Validation, the output instruction bytes. External pull-up resistors are required for program calibration. When the P 0 port is used to output the external memory of the low 8 bit map 1 address. Since this is a time-sharing output, the address data should be latched by an external latch, address latched, Signal Ale.