| 摘要 |
<p>PURPOSE:To attain writing of data to an EPROM without increasing the number of pins by adding a writing circuit to data input/output pins for connection to the EPROM and providing a control input circuit after separation of a data I/O. CONSTITUTION:Input/output pins P1-P4 of an I/O port 61 are connected to a data bus, i.e., an I/O via inverters 612, 614, 616 and 618 respectively and also to an end of an EPROM writing bus via inverters 611, 613, 615 and 617. Thus a writing circuit for EPROM is obtained. The other end of the EPROM writing bus is connected to the EPROM. While a reset pin Pi is used also as a pin for input of enable signal. When the enable signal is supplied through the Pi, the connection is secured among inverters 611-617. Thus the writing is carried out from the outside to the EPROM through pins P1-P4 respectively. At the same time, the inverters 612-618 are separated and the I/O is separated from the corresponding pin.</p> |
