Difference between revisions of "OSBYTE &6F"
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Revision as of 20:12, 8 March 2015
OSBYTE &6F (111) - Read/Write Aries/Watford Shadow RAM Switch
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+ and Master series use different shadow selection calls.
- OSBYTE &6C - Select Master 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