Difference between revisions of "OSBYTE &6F"
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[[Category:OSBYTE]] | [[Category:OSBYTE]] | ||
| − | OSBYTE &6F (111) - Read/Write Shadow RAM Switch | + | OSBYTE &6F (111) - Read/Write Aries/Watford Shadow RAM Switch |
X b7=0 no stack operation | X b7=0 no stack operation | ||
| Line 7: | Line 7: | ||
b6=1 read switch state | b6=1 read switch state | ||
b0=0 select video RAM | b0=0 select video RAM | ||
| − | b0=1 select | + | b0=1 select program RAM |
On exit, X contains the previous switch state: | On exit, X contains the previous switch state: | ||
b0=0 video RAM | b0=0 video RAM | ||
| − | b0=1 shadow | + | b0=1 program RAM |
| + | |||
| + | This gives the following entry and return values: | ||
| + | X=&00 - Select video RAM | ||
| + | &01 - Select program RAM | ||
| + | &40 - Read current RAM state | ||
| + | &41 - Read current RAM state | ||
| + | &80 - Save current RAM state and select video RAM | ||
| + | &81 - Save current RAM state and select program RAM | ||
| + | &C0 - Pop and select stacked RAM state | ||
| + | &C1 - Pop and select stacked RAM state | ||
| + | |||
| + | This call is implemented by the Watford and Aries shadow memory systems for | ||
| + | the BBC B computer, and compatible systems. The B+ and Master series use | ||
| + | different shadow selection calls. | ||
==See Also== | ==See Also== | ||
| + | * [[OSBYTE &6C]] - Select Master shadow memory | ||
| + | * [[OSBYTE &6F]] - Select BBC B shadow memory | ||
| + | * [[OSBYTE &70]] - Select memory for Master VDU access | ||
| + | * [[OSBYTE &71]] - Select memory for Master video display | ||
| + | * [[OSBYTE &72]] - Select future use of shadow memory | ||
| + | * [[OSBYTE &73]] - Select shadow bank | ||
| + | * [[OSBYTE &74]] - Check for Solidisk shadow memory | ||
| + | * [[Paging in video memory]] | ||
* http://mdfs.net/Docs/Comp/BBC/Osbyte00 | * http://mdfs.net/Docs/Comp/BBC/Osbyte00 | ||
| − | [[User: | + | [[User:WikiSysop|WikiSysop]] 00:23, 29 August 2013 (BST) |
Revision as of 00:23, 29 August 2013
OSBYTE &6F (111) - Read/Write Aries/Watford Shadow RAM Switch
X b7=0 no stack operation
b7=1 pop state from stack (reading), push state on stack (writing)
b6=0 write switch state
b6=1 read switch state
b0=0 select video RAM
b0=1 select program RAM
On exit, X contains the previous switch state:
b0=0 video RAM
b0=1 program RAM
This gives the following entry and return values:
X=&00 - Select video RAM
&01 - Select program RAM
&40 - Read current RAM state
&41 - Read current RAM state
&80 - Save current RAM state and select video RAM
&81 - Save current RAM state and select program RAM
&C0 - Pop and select stacked RAM state
&C1 - Pop and select stacked RAM state
This call is implemented by the Watford and Aries shadow memory systems for the BBC B computer, and compatible systems. The B+ and Master series use different shadow selection calls.
See Also
- OSBYTE &6C - Select Master shadow memory
- OSBYTE &6F - Select BBC B shadow memory
- OSBYTE &70 - Select memory for Master VDU access
- OSBYTE &71 - Select memory for Master video display
- OSBYTE &72 - Select future use of shadow memory
- OSBYTE &73 - Select shadow bank
- OSBYTE &74 - Check for Solidisk shadow memory
- Paging in video memory
- http://mdfs.net/Docs/Comp/BBC/Osbyte00
WikiSysop 00:23, 29 August 2013 (BST)
