DIGITAL INPUT/OUTPUT CIRCUIT

摘要

A digital input/output circuit to be connected between an internal data bus composed of 2 signal lines (n is zero or a positive integer) and 2 external terminals includes an output port for outputting data from the internal data bus to the external terminals and an input port for inputting the data from the external terminal to the internal data bus. The output port comprises a scrambler receiving data of 2 bits from the internal data bus and a mode signal and operating for relocating the received data in accordance with the mode signal so as to output the relocated data with each unit of 2 bits (m is an integer not greater than n) indicated by the mode signal. An output circuit includes 2 output buffers each having an input connected to receive directly or indirectly an output of the scrambler and an output connected to a corresponding one of the external terminals. This output circuit operates in response to the mode signal so as to make active 2 output buffers of the 2 output buffers in accordance with the mode signal and to make the other output buffers inactive. A data shifter is connected to the scrambler and includes data latch for latching data in accordance with the relocation pattern of the scrambler and shifting the latched data in accordance with the mode signal so that the data of 2 bits is outputted with each unit of 2 bits through the active output buffers.