Abstract: A serial input/output circuit with an automatic transfer function can easily re-transfer correct data even if a transfer error occurs during automatic transfer. When the transfer of one data has been completed, an automatic transfer data pointer normally automatically updates its contents and indicates an address in an automatic transfer RAM, which corresponds to data to be next transferred. An error generation active circuit makes an error control signal significant when an error detecting circuit detects an error produced in data or the occurrence of the error in the data is notified from a transfer opposite party. When the error control signal is made significant, the automatic transfer data pointer and the transfer counter do not update their values.

Abstract: A document edge detection apparatus that can detect document edges at high speed with good stability and precision, even when the documents have relatively large damaged portions, creases or smears, or have been scanned with a large skew angle.