Nintendo 1504166 - Game Boy Advance SP Edition Console Programming Manual page 149

AGB Programming Manual
RCNT [d03 - d00] Data Bit
When the corresponding terminal is set for input, the status(HI/LO) of the
terminal can be confirmed. If the corresponding terminal is set for output,
the status of the set bit is output.
©1999 - 2001 Nintendo of America Inc.
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Communication Functions
D.C.N. AGB-06-0001-002B4