Nintendo 1504166 - Game Boy Advance SP Edition Console Programming Manual page 135

AGB Programming Manual
At this point, the data output from the first slave is stored in the master and
each slave's SIOMULTI1 Register.
In this way, each slave is sent and all transmissions are carried out.
In the following situations the master produces a "SYNC Signal" (pull-up
input after the output of a 5 cycle HI interval of source oscillation) and the
transmission ends:
1. After the master outputs its own "Stop bit", the next "Start bit" is not
input after a certain period of time.
2. After a "Stop bit" is received from the first or second slave, a "Start bit"
is not input after a certain period of time.
3. A "Stop bit" is received from the third slave.
Once the transmission ends, the received data is stored in each of the
data registers (SIOMULTI0, SIOMULTI1, SIOMULTI2, and SIOMULTI3). If
there is a terminal that is not connected the initial data FFFFh is stored.
©1999 - 2001 Nintendo of America Inc.
135
Communication Functions
D.C.N. AGB-06-0001-002B4