| 摘要 |
<p>PURPOSE:To switch and to output the contents of a ROM and a register with a small area by setting an address line in a prescribed state by a control signal and controlling the connection between a bit line and an input port. CONSTITUTION:When a control signal C0 is set at L, transistors TRQ13-Q16 are turned off and a register 3 is separated from bit lines b1-b4 of a ROM cell array 1. Then the read output of the array 1 corresponding to the output values to address lines a1-a4 of an address decoder 2' is delivered. When the signal C0 is set at H, the outputs of 3-input NOR gates N11-N14 of the decoder 2' are all set at 0. Then all TRs in the array 1 are turned off, and the loads Q1-Q4 of the lines b1-b4 are equal to those of the connected circuits and then opened. AT the same time, the TRQ13-Q16 are turned on and the contents of the register 3 are delivered via the lines b1-b4. This eliminates a multiplexer for switching outputs, the corresponding wirings, etc. Thus it is possible to switch and output the contents of a ROM and a register with a small area.</p> |
