Difference between revisions of "OSBYTE &6F"

From BeebWiki
Jump to: navigation, search
(Added ROMSTROBE information.)
(Accidently overwitten with OSBYTE 6E.)
Line 1: Line 1:
 
[[Category:OSBYTE]]
 
[[Category:OSBYTE]]
===OSBYTE &6E (110) - Write to ROMSTROBE===
+
OSBYTE &6F (111) - Read/Write Aries/Watford Shadow RAM Switch
  
  On entry:
+
    On entry:
     X= new ROMSTROBE value
+
     X b7=0 no stack operation
  On exit:
+
      b7=1 pop state from stack (reading), push state on stack (writing)
     X= old ROMSTROBE value
+
      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
  
The value passed in X is written to the ROMSTROBE port and the RAM copy, the
+
This call is implemented by the Watford and Aries shadow memory systems for
old value of the RAM copy is returned. Implemented in the Electron Plus 1
+
the BBC B computer, and compatible systems. The B+, Integra-B and Master
Support ROM. The ROMSTROBE port is at &FC73 on the Electron, and writes
+
series use different shadow selection calls.
the byte of data while the ROMSTROBE line is activated on the cartridge
 
slot.
 
 
 
 
 
===OSBYTE &6E (110) - Early Watford DFS double-step control===
 
 
 
Do not use - use *OPT40,n and *OPT80,n.<ref>''The Micro User'', August 1986, p.22.</ref>
 
  
 
==See Also==
 
==See Also==
 +
* [[OSBYTE &49]] - Check for Integra-B shadow memory
 +
* [[OSBYTE &6C]] - Select Master/Integra-B 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
  
==References==
+
[[User:Jgharston|Jgharston]] ([[User talk:Jgharston|talk]]) 20:28, 3 April 2015 (UTC)
<references />
 
 
 
[[User:Jgharston|Jgharston]] 21:17, 26 May 2009 (UTC)
 

Revision as of 23:38, 14 February 2016

OSBYTE &6F (111) - Read/Write Aries/Watford Shadow RAM Switch

   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

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.

See Also

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