| 摘要 |
<p>PROBLEM TO BE SOLVED: To perform data write and data read control over an external storage device by using a general input/output port. SOLUTION: An input/output switching latch circuit 32 provided at an input/ output port part latches the address signal of an external RAM which is outputted to an input/output port part and outputs it from a port PY. When data are written, a port data latch circuit 30 of the input/output port part latches a data signal outputted to the data bus right after the address signal and outputs it from the port PY. The address signal is latched by an address latch circuit with an ALE signal outputted from a port PX and then an address of the external RAM is specified, so that the data are written in the specific address. When data are read out, the data are read out of the address specified according to the outputted address signal and this data signal is latched by an input data latch circuit 50 and outputted to the data bus.</p> |
