Expansion Bus Control Register

Number	TBRegisterNumber::$81
Readable	TBRegisterReadable::Yes
Writable	TBRegisterWritable::Yes
Short Description	ShortDesc::Expansion bus controls

Read (may change in the future):

Bit	Description
7	ROMCS is being asserted on the expansion bus
6	Expansion bus is currently enabled
5	Max clock is always propagated to the expansion bus
4	0 indicates the 48K rom is locked in place
3-2	Reserved
1-0	Max cpu speed while the expansion bus is enabled

Write (may change in the future):

Bit	Description
7	Make change immediate otherwise changes are noted for next soft reset
6	Enable the expansion bus (hard reset = 0)
5	Always propagate the max clock to the expansion bus (hard reset = 0)
4	0 to lock the 48k rom in place (hard reset = 0)
3-2	Reserved, must be 0
1-0	CPU speed when the expansion bus is enabled (currently fixed at 00 = 3.5 MHz) (hard reset = 00)

(note: Next registers with number higher than $7F are inaccessible from Copper code)