In telecommunication, a neutral direct-current telegraph system is a telegraph system in which (a) current flows during marking intervals and no current flows during spacing intervals for the transmission of signals over a line, and (b) the direction of current flow is immaterial. Synonymssingle-current system, single-current transmission system, single-Morse system.
... the United States.
However, because the GBA has no region lockout, European games will work fine on a U.S. GBA unit, and apparently, even a player who knows no Japanese ...