Expansion Bus Enable Register

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Revision as of 22:52, 4 December 2019 by Ped7g (talk | contribs) (core 3.0.5 changes/refresh)
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Number $80
Readable Yes
Writable Yes
Short Description Expansion bus controls/config

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)