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==Description==
The [[laplink cable|null-printer cable]] connects five output pins of a parallel port to five input pins on the other port, and vice versa. Due to the lack of an internal timing in the parallel ports, synchronization is done via software handshaking: of the five input or output pins, four are used for data transfer and one is used for synchronization. The [[Truth value|logical values]] at these pins can be read and written directly by the software via an io instruction.
Note that the method does NOT connect the bidirectional data lines from the two devices together, to avoid both lines being active at the same time. The status lines error, slct, papout, ack and busy on one device are connected to data pins d0 thru d4 respectively on the other.
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