DATA TRANSMISSION SYSTEM FOR KEY TELEPHONE SYSTEM

摘要

PURPOSE:To allow a pulse signal with polarity to correctly decode data regardless of the polarity of connecting a signal line through a pair of lines in terms of a key telephone set by detecting a change in a logical value, which is made by the bit of a specific logical value and further detecting the polarity that the bit of a reverse logical value shows in accordance with the former detection. CONSTITUTION:A start signal Ss inclduing a positive bit B1 as the bit of a specific logical value and negative bits B2 and B3 as the bits linked to said positive bit up to the prescribed order is returned. In an ST2 the change in the logical value due to the bit B 1 is detected by a change in a voltage in a negative direction. The poliarty shown by the bit B3 at a point t2 where 1.5 bits pass at a detection point t1 is detected. If it is negative, the connection polarity of the signal line 3 is judged to be regulated polarity. Whereas it is positive, the connection polarity is judged to be reverse. According to the judged result, the positive or negative logic of a transmission signal is selected.