Nintendo GAME BOY ADVANCE Programming Manual page 133

May 25, 2005
SIOCNT [d12] Transfer Length Setting Flag
Sets bit length of transfer data.
If 0, 8-bit transfer is carried out. If 1, 32-bit transfer is carried out.
SIOCNT [d07] Start Bit
With a setting of 1, a serial transfer starts. The bit is automatically reset after transfer completion.
SIOCNT [d03] Transfer Enable Flag Send
A setting of 0 enables transfer; 1 disables it.
This flag is output from the SO terminal until the start of a transfer. When the transfer starts, serial data
are output from the SO terminal.
SIOCNT [d02] Transfer Enable Flag Receive
It is possible to read the status of SI terminal (transfer-enable flag transmitting of the other party's hard-
ware) before communication starts.
It becomes invalid after communication has started.(receive data bit during communication is
reflected.)
SIOCNT [d01] Internal Shift Clock Selection
If 0, 256KHz is selected for the shift clock.
If 1, 2MHz is selected for the shift clock.
SIOCNT [d00] Shift Clock Selection
If 0, an external clock is used as a shift clock. (slave)
The external clock is input by the SC terminal from another hardware unit. SD terminal will go to LO
output.
If 1, an internal clock is used as a shift clock. (master)
The internal clock is output from the SC terminal, and SD terminal will be in the pull-up input status.
Cautions for Normal Serial Communications
The shift clock should be selected before the start bit of the SIOCNT register is set. Extra shift operations
may result if the serial transfer is started before or at the same time as the shift clock is selected.
Do not use a value of the transfer enable flag receiving bit for SIOCNT register while the start bit of SIO-
CNT register is being set. (Because it transforms to a receiving data bit that is being communicated.)
The 8 bit transfer mode is compatible in terms of modes with DMG/CGB, but the voltage with the commu-
nication terminal varies. Therefore, communication between Game Boy Advance and DMG/CGB is not
possible.
Using a Game Link cable for DMG/MGB is prohibited in normal serial communication mode. It is possible
to communicate at 256 KHz and 2 MHz with peripheral equipment that does not use a cable.
Always set a communication speed of 256 KHz when performing normal communication with the Game
Boy Advance Game Link cable. Communication cannot be done properly at 2 MHz.
Also, please note it will be a one-way communication due to cable connection of multi-play communication.
© 1999-2005 NINTENDO
8-Bit/32-Bit Normal Serial Communication
111
AGB-06-0001-002-B13
Released: May 27, 2005