| 摘要 |
<p>PURPOSE:To obtain a program memory which can recover to the previous condition instantaneously by providing a logic circuit to indicate the reading from the second ROM when the output signal of the block selection from a block selecting circuit exists and indicate the reading from the first ROM when the output signal does not exist. CONSTITUTION:When a memory reading indicating signal 8 and an address signal are sent from a CPU 1 and the correcting program to the selected block is not written in the second ROM 4, a reading indicating signal 10 is generated by logical gates 17-20, and when the signal 10 is effective, the program is read from the first ROM 3. When the correcting program is written in the second ROM 4, a reading indicating signal 11 is generated by logical gates 17-20. On the other hand, the address signal of the address belonging to the block of the second ROM 4 shown by the signal which comes to be H of the signal lines of Q1-Q32 by an encoder 14 is generated, and when the signal 11 is effective, the correcting program is read from the second ROM 4. Thus, the previous condition is recovered easily and the program can be efficiently corrected.</p> |
