| 摘要 |
<p>PURPOSE:To provide the microcomputer with the data bus precharging function which can stably judge whether or not an option peripheral device is mounted adaptively to an increase in the operation speed of the microcomputer and an increase in the load placed on a data bus. CONSTITUTION:This microcomputer is provided with a circuit which confirms whether or not the option peripheral device, extended and connected to the external data bus line of a CPU 11 at need is connected without switching a switch nor performing special operation. A CMOS transistor Q1 and a pull-up resistor R1 are provided between >=1 lines of the external data bus line Dn connected to the CPU l1 and a driving power source Vcc and the conduction control over the CMOS transistor is performed with output signals <RD> and R/<W> of the CPU. Under this conduction control, the transistor is turned ON in the read/write operation of the CPU and turned OFF in other cases. The response delay of signals on the data bus line Dn in option address read operation due to the increase in the load on the data bus line and an increase in parasitic capacity is improved by the precharging operation.</p> |
