OSBYTE &A0
OSBYTE &A0 (160) - Read VDU Variable, called by =VDU(n) from BASIC
This call returns variable number X in registers X and Y The VDU variables are stored in a machine-dependant location (&0300 in most 8-bit OSs), so this call should be made to read them. 16-bit values (eg &06/7) should be read by reading the low numbered location (eg &06).
As the VDU variables number 0 to 127, some platforms translate VDU variable numbers 128+ to the appropriate RISC OS OS_ReadVduVariables offset.
VDU Variables
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&00/1 Current graphics window left column in pixels
&02/3 Current graphics window bottom row in pixels
&04/5 Current graphics window right column in pixels
&06/7 Current graphics window top row in pixels
&08 Current text window left hand column
&09 Current text window bottom row
&0A Current text window right hand column
&0B Current text window top column
&0C/D Current graphics X origin in external coordinates
&0E/F Current graphics Y origin in external coordinates
&10/1 Current graphics X position in external coordinates
&12/3 Current graphics Y position in external coordinates
&14/5 Old graphics X position in external coordinates
&16/7 Old graphics Y position in external coordinates
&18 Current text X position (=POS)
&19 Current text Y position (=VPOS)
&1A Line within current graphics cell of graphics cursor
&1B Graphics workspace/VDU queue
&1F-&23 VDU queue
&24/5 Current graphics X position in internal coordinates
&26/7 Current graphics Y position in internal coordinates
&28-&2F Bitmap read from screen by OSBYTE 135
&30-&49 Graphics workspace
&4A/B Text cursor address for 6845
&4C/D Text window width in bytes
&4E High byte of bottom of screen memory, readable as
vdu variable &4D AND &FF00
&4F Bytes per character for current mode
&50/&51 Screen display start address for 6845
&52/&53 Bytes per screen row
&54 Screen memory size high byte, readable as vdu
variable &53 AND &FF00
&55 Current screen mode (=MODE)
&56 Memory map type
0 - 20K mode
1 - 16K mode
2 - 10K mode
3 - 8K mode
4 - 1K mode
&57 Foreground text colour
&58 Background text colour
&59 Foreground graphics colour
&5A Background graphics colour
&5B Foreground plot mode
&5C Background plot mode
&5D/&5E General VDU jump vector
&5F Cursor start register previous setting
&60 Number logical colours -1
&61 Pixels per byte -1 (zero if text only mode)
&62 Leftmost pixel colour mask
&63 Rightmost pixel colour mask
&64 Text input X position
&65 Text input Y position
BBC, Electron: Master:
&66 Teletext output cursor character VDU 23,16 setting
&67 Font explosion flags, b1=224-255 VDU 23,6 dot pattern
in RAM, b7=32-63 in RAM
&68 Font location, characters 32-63 Current dot pattern state
&69 Font location, characters 64-95 Colour plotting ECF pattern
number or zero
&6A Font location, characters 96-127 Graphics foreground ECF
pattern number or zero
&6B Font location, characters 128-159 Graphics background ECF
pattern number or zero
&6C Font location, characters 160-191 b7 set when cursor off
righthand edge of screen
&6D Font location, characters 192-223 Graphics foreground colour
&6E Font location, characters 224-225 Graphics background colour
&6F-&7E Palette for colours 0 to 15
&7F Unused
See Also
Jgharston 22:15, 26 May 2009 (UTC)
