Describe serial interrupt in serial interrupt section

[quinnyo]

This removes the (out of place) description of the serial port from the 'Interrupt Sources' page and replaces it with a description of when the serial interrupt is requested (which is the main thing that should be there).

This fixes #528, but I haven't moved any of the deleted text to the Serial Data Transfer page. It was almost all redundant. I don't think we're losing anything.

[ISSOtm]

Here's what I think they are intended to mean:

The state of the last bit shifted out determines the state of the output line until another transfer takes place.

This is saying that the last bit emitted on the bus "sticks" until the next clock cycle, instead of e.g. briefly pulsing one way or another.

The Game Boy does not support wake-on-LAN. Completion of an externally clocked serial transfer does not exit STOP mode.

I'd guess that the serial circuitry still functions in STOP mode (since it's essentially async from the rest of the system?), but does not exit STOP mode?

[pinobatch]

"Wake-on-LAN" refers to a feature by which an Ethernet adapter can bring a PC out of its counterpart to STOP mode. If there were a way to wake an externally clocked Game Boy through the serial port, some specialized uses would become possible.

[quinnyo]

Thanks for the feedback!
I see no reason to port either statement over.

Details

The state of the last bit shifted out determines the state of the output line until another transfer takes place.

This is a detail of the electronics and is the most obvious way that serial communication is implemented -- the signal level is only changed once for each bit, on the leading edge of each clock pulse. This is the default, simple, obvious way to do it. To do otherwise would "break the contract" with the connected device.

The Game Boy does not support wake-on-LAN. Completion of an externally clocked serial transfer does not exit STOP mode.

Mentioning wake-on-LAN out of nowhere is confusing. It also suggests the Game Boy has some sort of networking capability, but is lacking that feature.
The list of events and conditions that don't terminate stop mode may well be endless.