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writing_20to_20vdu_20variables

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writing_20to_20vdu_20variables [2018/03/31 13:19]
127.0.0.1 external edit
writing_20to_20vdu_20variables [2018/04/16 14:39] (current)
richardrussell Tidied up formatting
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 =====Writing to VDU variables===== =====Writing to VDU variables=====
  
-//by Richard Russell, April 2009//\\ \\  The main [[http://​www.bbcbasic.co.uk/​bbcwin/​manual/​bbcwin2.html#​vduvars|Help documentation]] recommends that the **VDU variables** be treated as //​read-only//​ values, which are modified only by means of the related VDU commands or associated keywords. However, to achieve certain special effects, or in advanced applications,​ it may be appropriate to write to those variables. This should be done with care, if unwanted side-effects are not to result.\\ \\  The table below lists the **VDU variables**,​ why you might want to write to them, and the main precautions which need to be considered when doing so:\\ \\ +//by Richard Russell, April 2009//\\ \\  The main [[http://​www.bbcbasic.co.uk/​bbcwin/​manual/​bbcwin2.html#​vduvars|Help documentation]] recommends that the **VDU variables** be treated as //​read-only//​ values, which are modified only by means of the related VDU commands or associated keywords. However, to achieve certain special effects, or in advanced applications,​ it may be appropriate to write to those variables. This should be done with care, if unwanted side-effects are not to result.\\ \\  The table below lists the **VDU variables**,​ why you might want to write to them, and the main precautions which need to be considered when doing so:
  
 ^ Variable(s)\\ ^ Reason(s) to write\\ ^ Precautions\\ ^ ^ Variable(s)\\ ^ Reason(s) to write\\ ^ Precautions\\ ^
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 | @vdu.m.c&​\\ | Set insert/​overtype mode (bit 0) in INPUT replacement,​ e.g. see NOWAIT.BBC\\ | Change bit(s) '​atomically'​ using OR= or AND= (or assembler equivalents)\\ | | @vdu.m.c&​\\ | Set insert/​overtype mode (bit 0) in INPUT replacement,​ e.g. see NOWAIT.BBC\\ | Change bit(s) '​atomically'​ using OR= or AND= (or assembler equivalents)\\ |
 | @vdu.m.d&​\\ | Set scrolls-until-pause independently of text viewport height\\ | 0 = no paging, &80+n = pause after n scrolls\\ | | @vdu.m.d&​\\ | Set scrolls-until-pause independently of text viewport height\\ | 0 = no paging, &80+n = pause after n scrolls\\ |
-\\  ​This article is not intended to be exhaustive; side-effects not mentioned here may be experienced when writing to **VDU variables**. Do so at your own risk.+ 
 +This article is not intended to be exhaustive; side-effects not mentioned here may be experienced when writing to **VDU variables**. Do so at your own risk.
writing_20to_20vdu_20variables.txt · Last modified: 2018/04/16 14:39 by richardrussell