| 摘要 |
PURPOSE:To perform the communication independently of phase in the single-phase three-wire system and perform the access control in a relatively high speed by superposing the modulation output onto power source waves of a U-phase two-wire line and a V-phase two-wire line to transmit it to both lines and monitoring their received outputs in each computer communication station to control the transmission right. CONSTITUTION:A frequency converting circuit 42 of a head end device 4 converts two- phase PSK data signals of a carrier frequency F1, which are transmitted to power supply lines 11 and 12 from communication stations 21-2N and 31-3M, to two-phase PSK (phase shift keying) data signals of a carrier frequency F2 different from said F1 and transmits them to power supply lines 11 and 12. When each of communication stations 21-2N and 31-3M has its own transmission request, it transmits two-phase PSK data signals with the carrier frequency F1 and monitors two-phase PSK data signals, which are converted to the carrier frequency F2 and are turned back from the head end device 4, to detect the collision with another communication station; and if the collision is detected, the communication station stops the data transmission by itself and transmits data again after a prescribed time in accordance with certain procedures. |
