A differential TTL signal consists of two such wires, also referenced to a system ground.
The principle is similar to that of low-voltage differential signaling (LVDS), but with different voltage levels.
[4] In a long cable, stray electromagnetic fields in the environment, or stray currents in the system ground, can induce unwanted voltages that cause errors at the receiver.
This arrangement prevents the signal from injecting currents into the ground connection, which might upset other circuits attached to it.
[citation needed] Differential TTL signaling was used in the Serial Storage Architecture (SSA) standard devised by IBM,[citation needed] but this is mostly obsolete.