Difference between revisions of "OSBYTE &6C"

From BeebWiki
Jump to: navigation, search
m (1 revision)
m (See Also)
(8 intermediate revisions by 2 users not shown)
Line 1: Line 1:
 
[[Category:OSBYTE]]
 
[[Category:OSBYTE]]
OSBYTE &6C (108) - Main/Shadow RAM Usage
+
{{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
  
    Y=0 X=0 Main memory appears from &3000 to &7FFF
+
This has immediate effect and allows the user to access the shadow display
        X=1 Shadow memory appears from &3000 to &7FFF
+
memory, for instance, to load or save it or manipulate it directly. The
    This has immediate effect and allows the user to make use of the 20k of
+
memory that is accessed by the Master VDU drivers and displayed can set with
    extra RAM for other purposes.
+
[[OSBYTE &70]] and [[OSBYTE &71]].
  
==See Also==
+
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
 
* http://mdfs.net/Docs/Comp/BBC/Osbyte00
  
[[User:Jgharston|Jgharston]] 21:15, 26 May 2009 (UTC)
+
----
 +
[[User:Jgharston|Jgharston]] ([[User talk:Jgharston|talk]]) 01:12, 14 January 2016 (UTC)

Revision as of 19:27, 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


Jgharston (talk) 01:12, 14 January 2016 (UTC)