Data communication apparatus for maintaining data integrity during an

Abstract

In a data communication apparatus, when detecting a 'catch phone' signal sent out from an exchange, a receiving station requests a transmitting station to resend data by use of protocol information. At the transmitting station, the data resending request is detected in a protocol information analyzing unit, and a predetermined unit of data which was transmitted immediately before the present time is resent. The receiving station has a page deleting unit to save the memory area used to store the data resent and avoid printing of unnecessary data. The page deleting unit enables deletion of data received when a 'catch phone' call comes in and permits the resent data to be effectively stored in a memory. Also, in the apparatus, a 'catch phone' detecting unit in a transmitting station detects that a circuit connection request comes in from a third station on the basis of a 'catch phone' signal sent out from an exchange. A page-end detecting unit detects completion of transmission of a predetermined unit of data. A condition judging unit automatically decides whether to open the circuit or not on the occasion of resending data in accordance with the state of a 'catch phone' detecting signal 'a' and a page-end detecting signal 'b'. If the page end is detected in a short time after the detection of a 'catch phone' signal, the circuit is not opened. If the 'catch phone' signal has continued when the page end is detected, after the circuit is temporarily opened, resending of data is executed.