| 摘要 |
PURPOSE:To realize a change of contents of an ROM in a real-time working mode without discontinuing the working of a CPU when the contents of ROM is changed, by adding an ROM change discrimination circuit. CONSTITUTION:A CPU1 is connected to an address bus 4, a data bus 5 and a control bus 6. The 1st and 2nd ROMs 21 and 22 are connected to the bus 5, and then a decoder 3 is connected to the buses 4 and 6 along with a connection of an ROM change discrimination circuit 9. An ROM setting circuit 8 is connected to the circuit 9 via an ROM change set signal transmission line 11 and an ROM changeover signal line 12, and a selection control line changeover circuit 10 is connected to a ROM selection control line 7 at the output side of the decoder 3. Then the ROM which is usually used is defined as an ROM21, and an ROM22 is used for a change of contents of ROM21. During this change of contents, the setting conditions of the circuit 8 is compared and discriminated with the conditions given from then CPU1. Then the circuit 10 is switched to change the contents of ROM21, and the working is continued by the ROM22. |
