Difference between revisions of "Expansion Bus Control Register"
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(Ped7g moved page Expansion Bus Control Register to Expansion Bus Enable Register: core 3.0.5 change/refresh) (Tag: New redirect) |
m (core 3.0.5 changes/refresh) (Tag: Removed redirect) |
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| − | + | {{NextRegister | |
| + | |Number=$81 | ||
| + | |Readable=Yes | ||
| + | |Writable=Yes | ||
| + | |ShortDesc=Expansion bus controls | ||
| + | }} | ||
| + | Read (may change in the future): | ||
| + | {|class="wikitable" | ||
| + | ! 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): | ||
| + | {|class="wikitable" | ||
| + | ! 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) | ||
Revision as of 23:53, 4 December 2019
| Number | $81 |
|---|---|
| Readable | Yes |
| Writable | Yes |
| Short Description | 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)