Serial transfer control information edit

[jbshelton]

More testing needs to be done, but at the moment with my previous experience, bit 7 of $FF02 (SB) needs to be set in order for the Gameboy to accept an external clock and start shifting in/out data- it is mandatory, not optional as the page implies.

[quinnyo]

This is my understanding of it too.
Bit 7 of the SC register can be thought of as enabling/disabling the whole serial port. The serial port has to be enabled to respond to clock pulses. A disabled serial port can't be turned on remotely.

[ISSOtm]

This also matches my own experimenting with serial, yes. I think this is fine to add to the Serial page without further testing.