I have been recently coding some serial transfer routines and have found a
few interesting things that I thought may be useful to anyone also
contemplating doing link up.

Keeping the two gameboys in sync is the most difficuly things to do as the
vblanks are almost always different.

A few things to bear in mind:

* Always delay the data by one frame.  This gives an entire frame for
transfer to occur which is good if one machine is behind.
* Strangely, on performing a serial transfer (SC register set to $81) the
serial interrupt occurs on the master first and then the slave.
* On peforming a transfer and no machine is linked then SB will be $FF
* On peforming a transfer and a machine is linked but swiched OFF then SB
will be $0 (must be due to ground pin)
* On peforming a transfer and a machine is linked but slave is in an
interrupt then SB will be $FF
* Keep all interrupt code as short as possible.
* Be careful when using AC adaptors on gameboy Pockets as this sometimes
causes interference on the serial port.


If anyone is interested I may make my serial link code for GBDK(but using
asm for interrupts) public.


Hopefully this info helps someone at there in Game Boy land.......

Cheers

Ian.