PO port is a set of 8 open drain open type bidirectional 1/O port, which is also the address / data bus multiplexing port. As an output port, can absorb the current Yu Mei 8 Ding FL gate, written to port "1" can be used as high impedance inputs. During accesses to external program and data memory memory, this group of daily time conversion (low 8) address and data bus multiplexing, activate the internal pull ups during the visit. In the Flash programming, PO port receives the code bytes during program verification, and outputs the code bytes, check, require external pull resistance