Difference between revisions of "OSBYTE &6C"
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[[Category:OSBYTE]] | [[Category:OSBYTE]] | ||
| − | OSBYTE &6C (108) - Main/Shadow RAM access | + | {{PageTitle|OSBYTE &6C (108) - Main/Shadow RAM access}} |
| + | On entry: | ||
| + | X=0 Master: Main memory appears from &3000 to &7FFF | ||
| + | Integra-B: Non-display memory appears from &3000 to &7FFF | ||
| + | X<>0 Master: Shadow memory appears from &3000 to &7FFF | ||
| + | Integra-B: Display memory appears from &3000 to &7FFF | ||
| + | On exit: | ||
| + | X preserved | ||
| − | + | This has immediate effect and allows the user to access the shadow display | |
| − | + | memory, for instance, to load or save it or manipulate it directly. The | |
| − | + | memory that is accessed by the Master VDU drivers and displayed can set with | |
| − | |||
| − | |||
| − | |||
| − | This has immediate effect and allows the user to access the | ||
| − | |||
| − | that is accessed by the Master VDU drivers and displayed can set with | ||
[[OSBYTE &70]] and [[OSBYTE &71]]. | [[OSBYTE &70]] and [[OSBYTE &71]]. | ||
Shadow RAM on the BBC B with the Integra-B system is also paged in with | Shadow RAM on the BBC B with the Integra-B system is also paged in with | ||
| − | OSBYTE &6C. | + | OSBYTE &6C. Note that the Integra-B functions subtly differently to the |
| + | Master. If a shadow screen mode is being displayed the Integra-B functions | ||
| + | the same as the Master. If a non-shadow screen mode is being displayed, the | ||
| + | action is the opposite to the Master. | ||
On the BBC B+ the displayed memory is always the bank selected with MODE or | On the BBC B+ the displayed memory is always the bank selected with MODE or | ||
[[OSBYTE &72]], and the user can only access the shadow memory by calling | [[OSBYTE &72]], and the user can only access the shadow memory by calling | ||
[[OSRDSC]]. | [[OSRDSC]]. | ||
| + | |||
| + | The Aries and Watford systems use [[OSBYTE &6F]]. | ||
==See also== | ==See also== | ||
* [[OSBYTE &49]] - Check for Integra-B shadow memory | * [[OSBYTE &49]] - Check for Integra-B shadow memory | ||
* [[OSBYTE &6C]] - Select Master/Integra-B shadow memory | * [[OSBYTE &6C]] - Select Master/Integra-B shadow memory | ||
| − | * [[OSBYTE &6F]] - Select | + | * [[OSBYTE &6F]] - Select Aries/Watford shadow memory |
* [[OSBYTE &70]] - Select memory for Master VDU access | * [[OSBYTE &70]] - Select memory for Master VDU access | ||
* [[OSBYTE &71]] - Select memory for Master video display | * [[OSBYTE &71]] - Select memory for Master video display | ||
| Line 32: | Line 38: | ||
* http://mdfs.net/Docs/Comp/BBC/Osbyte00 | * http://mdfs.net/Docs/Comp/BBC/Osbyte00 | ||
| − | [[User:Jgharston|Jgharston]] ([[User talk:Jgharston|talk]]) 01: | + | ---- |
| + | [[User:Jgharston|Jgharston]] ([[User talk:Jgharston|talk]]) 01:12, 14 January 2016 (UTC) | ||
Revision as of 20:27, 22 January 2021
OSBYTE &6C (108) - Main/Shadow RAM access
On entry:
X=0 Master: Main memory appears from &3000 to &7FFF
Integra-B: Non-display memory appears from &3000 to &7FFF
X<>0 Master: Shadow memory appears from &3000 to &7FFF
Integra-B: Display memory appears from &3000 to &7FFF
On exit:
X preserved
This has immediate effect and allows the user to access the shadow display memory, for instance, to load or save it or manipulate it directly. The memory that is accessed by the Master VDU drivers and displayed can set with OSBYTE &70 and OSBYTE &71.
Shadow RAM on the BBC B with the Integra-B system is also paged in with OSBYTE &6C. Note that the Integra-B functions subtly differently to the Master. If a shadow screen mode is being displayed the Integra-B functions the same as the Master. If a non-shadow screen mode is being displayed, the action is the opposite to the Master.
On the BBC B+ the displayed memory is always the bank selected with MODE or OSBYTE &72, and the user can only access the shadow memory by calling OSRDSC.
The Aries and Watford systems use OSBYTE &6F.
See also
- OSBYTE &49 - Check for Integra-B shadow memory
- OSBYTE &6C - Select Master/Integra-B shadow memory
- OSBYTE &6F - Select Aries/Watford 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
