TELETEXT RECEIVER WITH REMOVABLE MEMORY EXPANSION CARD

摘要

PURPOSE:To prevent runaway of a CPU or its malfunction even if a card is inserted or taken out suddenly by always outputting a check signal to a system microcomputer of a video/audio switching control section from a timer so as to detect the presence of a ROM on the card at a prescribed period. CONSTITUTION:A system microcomputer 13 of a video/audio switching control section 3 uses a check signal from a timer 41 to always monitor the presence of a signal from an expansion ROM presence/absence terminal 40 of a memory expansion card 7 and selects a PROM 22 of a teletext processing section 4 instantly when the takeout of the memory expansion card 7 is detected and outputs a reset signal to a CPU 21. Thus, runaway is prevented. Even if the memory expansion card 7 is suddenly inserted, the system microcomputer 13 of the video/audio switching control section 3 detects the presence of a signal from the expansion ROM presence/absence terminal 40 of the memory expansion card 7 and resets the CPU 21 once to prevent malfunction.