| 摘要 |
PURPOSE:To observe easily the state of an inner data bus of a single-chip microcomputer by using a logical circuit to obtain an OR between read and write control signals and opening outside an extension port with the output of said logical circuit. CONSTITUTION:When a CPU12 performs reading actions to inner RAMs 14 and 16, an inner read control signal Ri is applied to a bi-directional buffer 18 via logical circuits G1 and G2. In this case, the G2 is activated by a test mode selection signal R given from outside. Thus the buffer 18 is opened outside. In other words, the state of an inner data bus DB is delivered outside via a data port Pb for extension. In a write mode the buffer 18 is also opened outside by the signal Ri and a logical circuit G3. That is, the conflict is avoided between write and read control signals at the buffer 18. Thus the buffer 18 delivers outside the state of the bus DB even in an inner read mode for easy observation of said state of the DB. |
