Difference between revisions of "Layer 2 Access Port"
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|Number=$123B | |Number=$123B | ||
|ShortDesc=Enables [[Layer 2]] and controls paging of layer 2 screen into lower memory. | |ShortDesc=Enables [[Layer 2]] and controls paging of layer 2 screen into lower memory. | ||
| − | |Readable= | + | |Readable=Yes |
| − | |Writable= | + | |Writable=Yes |
|Subsystem=Layer 2 | |Subsystem=Layer 2 | ||
|PortMask=%0001 0010 0011 1011 ?? | |PortMask=%0001 0010 0011 1011 ?? | ||
}} | }} | ||
| + | {| class="wikitable" | ||
| + | ! Bit !! Description | ||
| + | |- | ||
| + | | 7-6 || Video RAM bank select (write/read paging) | ||
| + | |- | ||
| + | | 5-4 || Reserved, write 0 | ||
| + | |- | ||
| + | | 3 || Use Shadow Layer 2 for paging - {{NextRegNo|$13}} | ||
| + | |- | ||
| + | | 2 || Enable Layer 2 read-only paging | ||
| + | |- | ||
| + | | 1 || Layer 2 visible - {{NextRegNo|$12}} | ||
| + | Since core 3.0 this bit has mirror in {{NextRegNo|$69}} | ||
| + | |- | ||
| + | | 0 || Enable Layer 2 write-only paging | ||
| + | |} | ||
Revision as of 20:17, 27 November 2019
| Number | $123B |
|---|---|
| Decimal | |
| Short desc. | Enables Layer 2 and controls paging of layer 2 screen into lower memory. |
| Bit Mask | %0001 0010 0011 1011 ?? |
| Readable | Yes |
| Writable | Yes |
| Subsystem | Layer 2 |
| Bit | Description |
|---|---|
| 7-6 | Video RAM bank select (write/read paging) |
| 5-4 | Reserved, write 0 |
| 3 | Use Shadow Layer 2 for paging - Layer 2 RAM Shadow Page Register ($13) |
| 2 | Enable Layer 2 read-only paging |
| 1 | Layer 2 visible - Layer 2 RAM Page Register ($12)
Since core 3.0 this bit has mirror in Display Control 1 Register ($69) |
| 0 | Enable Layer 2 write-only paging |