Difference between revisions of "OSBYTE &6F"

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(Added ROMSTROBE information.)
(Accidently overwitten with OSBYTE 6E.)
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[[Category:OSBYTE]]
 
[[Category:OSBYTE]]
===OSBYTE &6E (110) - Write to ROMSTROBE===
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OSBYTE &6F (111) - Read/Write Aries/Watford Shadow RAM Switch
  
  On entry:
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    On entry:
     X= new ROMSTROBE value
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     X b7=0 no stack operation
  On exit:
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      b7=1 pop state from stack (reading), push state on stack (writing)
     X= old ROMSTROBE value
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      b6=0 write switch state
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      b6=1 read switch state
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      b0=0 select video RAM
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      b0=1 select program RAM
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    On exit, X contains the previous switch state:
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      b0=0 video RAM
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      b0=1 program RAM
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    This gives the following entry and return values:
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     X=&00 - Select video RAM
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      &01 - Select program RAM
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      &40 - Read current RAM state
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      &41 - Read current RAM state
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      &80 - Save current RAM state and select video RAM
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      &81 - Save current RAM state and select program RAM
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      &C0 - Pop and select stacked RAM state
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      &C1 - Pop and select stacked RAM state
  
The value passed in X is written to the ROMSTROBE port and the RAM copy, the
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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
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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
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series use different shadow selection calls.
the byte of data while the ROMSTROBE line is activated on the cartridge
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slot.
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===OSBYTE &6E (110) - Early Watford DFS double-step control===
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Do not use - use *OPT40,n and *OPT80,n.<ref>''The Micro User'', August 1986, p.22.</ref>
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==See Also==
 
==See Also==
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* [[OSBYTE &49]] - Check for Integra-B shadow memory
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* [[OSBYTE &6C]] - Select Master/Integra-B shadow memory
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* [[OSBYTE &6F]] - Select BBC B shadow memory
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* [[OSBYTE &70]] - Select memory for Master VDU access
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* [[OSBYTE &71]] - Select memory for Master video display
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* [[OSBYTE &72]] - Select future use of shadow memory
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* [[OSBYTE &73]] - Select shadow bank
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* [[OSBYTE &74]] - Check for Solidisk shadow memory
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* [[Paging in video memory]]
 
* http://mdfs.net/Docs/Comp/BBC/Osbyte00
 
* http://mdfs.net/Docs/Comp/BBC/Osbyte00
  
==References==
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[[User:Jgharston|Jgharston]] ([[User talk:Jgharston|talk]]) 20:28, 3 April 2015 (UTC)
<references />
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[[User:Jgharston|Jgharston]] 21:17, 26 May 2009 (UTC)
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Revision as of 00:38, 15 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)