Patent ID: 7821850

Claim:
A semiconductor digital circuit performing data transfer between first and second circuit areas operating at different power supply voltages and different operation clocks, wherein the semiconductor digital circuit is disposed on a boundary between said first and second circuit areas, and the circuit includes circuit elements that perform interconversions between different signal voltage levels of said first and second circuit areas, the semiconductor digital circuit comprising: a plurality of data entry registers that hold data; entry management flag circuits that manage the presence or absence of effective data in each of said plurality of said data entry registers; a write entry management circuit that specifies an entry to which data are written out of said data entry registers; a read entry management circuit that specifies an entry from which data are read out of said data entry registers; an output selector that selects one of contents in the data entry registers according to an instruction from said read entry management circuit and outputs the selected content; and voltage level converting circuits that mutually convert signal voltage levels of each of said first and second circuit areas; and wherein said voltage level converting circuits are respectively provided between outputs of said data entry registers and inputs of said output selector, and inside said entry management flag circuits.