Difference between revisions of "OSBYTE &6F"

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m (Added title, slight rewording.)
m (See Also)
 
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       &C1 - Pop and select stacked RAM state
 
       &C1 - Pop and select stacked RAM state
  
==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

Latest revision as of 19:27, 22 January 2021

OSBYTE &6F (111) - Aries/Watford Shadow RAM access

This call is implemented by the Watford and Aries shadow memory systems for the BBC B computer, and compatible systems. The B+, Integra-B and Master series use different shadow selection calls.

   On entry:
   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

See also


Jgharston (talk) 20:28, 3 April 2015 (UTC)