| 摘要 |
PURPOSE:To check data from ROM by a simple mechanism to provide checking function to a computer by selecting the data from internal data bus or the output from a comparator in accordance with the command to send the selected data to the output terminal. CONSTITUTION:A controlling terminal 2 of a microcomputer is applied with an input of L-level during the normal operation and an input of H-level when an internal ROM13 is checked to control multiplexers 9, 10. The multiplexer 10 is connected with an internal data bus 6 through an instruction decoder 14 and connected further with an internal ROM13 and a comparator 7. The multiplexer 9 is connected with multiplexers 11, 9 in series and the multiplexer 9, 11, 8 are connected respectively to the bus 6. The input signal from an input terminal 3 is sent through the multiplexer 8 into a comparator 7. The multiplexer 9 selects the outputs from the bus 6 and from a program counter 12 and sends the selected output to an output terminal 4. The multiplexer 11 selects the output from the bus and from the comparator 7 and sends the selected output to an output terminal 5 for checking the data from the ROM13. |
