| 摘要 |
PURPOSE:To read out a PROM data without increasing external terminal pins even when plural sets of PROMs exist by adding a gate function to the output buffer circuit of a PROM storing a defective address. CONSTITUTION:If the transistor Q10 of the buffer circuit 30A is turned off by a control circuit 26 that operates in response to an output prohibiting signal, the transistors Q1 and Q2 of a current switch are respectively turned on and off. Accordingly, the PROM storing a defective address 20 can not output its content to a common reading circuit 28 via the circuit 30A. It is the same as with a PROM 22, and only the content of the selected ROM 20 or 22 is read out by the circuit 28. As a result, at the time of such as a reading for content-updating, the reading of the PROM can be executed without increasing the external terminal pins even when the plural PROMs exist on the same chip.
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