| 摘要 |
<p>PURPOSE:To make a nonvolatile memory readable by opening a gate circuit only when a digital output coincident with a bit pattern set by hardware is supplied to a CPU. CONSTITUTION:Even if a write signal is supplied from the CPU to a write pulse line 10, this circuit does not perform writing operation unless a gate circuit 5 interposed between the circuit and a terminal W is open. Namely, the gate circuit 5 is opened only when the CPU outputs the predetermined special bit pattern to supply the digital output write signal 14 to a latch circuit 2 and the special bit pattern is latched in a latch circuit 2 to output a coincidence signal from a coincidence circuit 3 to an output 11 when the output of a special bit pattern generator 4 coincides with the output of the latch circuit 2. The latch circuit 2 is supplied with a clear signal at a line 25 through hardware when the system is started, and the contents of the clear circuit are all cleared.</p> |
