Nintendo GAME BOY Programming Manual page 31

2.5.2 Serial Cable Communication: Reference flowchart
Flow until start of game
Start
(SB) Slave Code
RD Clear
(SC) $80
2P Start?
Y
Transfer
RD = Master Code?
N
RD = Slave Code?
N
N
V_BLANK?
Y
Transfer
(SB) Slave Code
(SC) $81
RET
-Select code other than $00 and $FF. (For both slave and
master code).
-Clear the receive data buffer (RD).
-Both sides wait in receive-wait status.
N
-Game on which Start key pressed first becomes master by
sending master code to other game.
Y
-Game first notified that it is slave by master code
Slave Start
sent from master. Subsequently moves to game flow.
Y
-Data sent when this side becomes master is the slave
Master Start
code. Game subsequently moves to game flow.
SIO Interrupt
RD
RD = Slave Code?
(SB)
1ms WAIT
(SC)
RETI
31
(SB)
TD: Transfer
TD Data Buffer
Timing of
receive
synchronized
with Power Up.
$80
Chapter 1: System