| 摘要 |
<p>PURPOSE:To discriminate simply types of a mask ROM products by checking a voltage level of an external terminal in a static condition direct current like by separating at least one external terminal from an additive memory cell when a control signal is not present. CONSTITUTION:When a test signal is added to a test terminal T3, a change over circuit U1 connects a signal line L2 and a signal line L3 and separates a signal line L1 from a signal line L3. A test circuit U2 is produced by the same mask as using in a diffusion in accordance with a discrimination number of a ROM code. The test circuit U2 is operated by a voltage applied to the terminal T3, in a testing condition, a switch S1 is closed by the test signal of a signal line L4. When a switch S2 is opened by a diffusing mask, a voltage level of the signal line L becomes high and observed by an external terminal T2 through the change over circuit U1 Thereby the ROM code discriminating number can be discriminated by a simple device and an operation efficiency is raised.</p> |
