OSBYTE &A3

OSBYTE &A3 (163) - Application support

 On entry:
   X = application identifier
       X=tba Font control
       X=128 Electron Plus 1
       X=192 Acornsoft Pascal
       X=241 Acornsoft LOGO
       X=242 Graphics Extension Support
       X=243 65Tube
       X=253 Cause a reset
       X=254 unknown
       X=255 Acornsoft View family
   Y = parameter
 On exit:
   X = return value
   Y = return value

X=&80 (128) Plus 1 Support

 On entry:
   Y=0 enable printer/ADC
   Y=1 disable printer/ADC
   Y=2 enable serial port
   Y=3 disable serial port
   Y=4 restore ROM table
 On exit:
   If Y<4 on entry,
     X=0 if enabled, X<>0 if disabled
   If Y=4 on entry,
     X=default language in X, b7 set if no default language

X=&81 (129) Sideways RAM font control (OS 1.50)

 On entry:
   Y=sideways RAM bank to contain fonts
 On exit:
   X,Y preserved

X=&82 to &88 (130 to 136) Font page control (OS 1.50)

 On entry:
   X=129+font page number (1 to 7, i.e. char codes DIV 32)
   Y=0 set font page soft (RAM)
   Y=1 set font page hard (ROM)
   Y=2 copy current page to RAM (no effect if soft)
   Y=3 reserved
   Y>3 set font page soft and RAM page number to Y
 On exit:
   X,Y preserved

X=&C0 (192) Acornsoft Pascal

 On entry:
   Y=0     enter language ROM of twin ROM set
   Y=1
   Y=2
   Y=3

Acornsoft Pascal is supplied as two 16K ROMs, one is the language code, and the other is support code, including the *Command parser. When the *PASCAL command is matched, or if the support code is entered as a language it, issues OSBYTE 163,192,0 to cause the other ROM to start itself.

X=&F1 (241) Acornsoft LOGO

 On entry:
   Y=0     enter language ROM of twin ROM set
   Y=1
   Y=2
   Y=3
   Y=4

Acornsoft LOGO is supplied as two 16K ROMs, one is the language code, and the other is support code, including the *Command parser. When the *LOGO command is matched, or if the support code is entered as a language it, issues OSBYTE 163,241,0 to cause the other ROM to start itself.

X=&F2 (242) Graphics Extension Support (GSX, RISC OS)

 On entry:
   Y=0     resets the dot-dash pattern and length to defaults
   Y=1..64 set dot dash pattern repeat length
 On entry:
   Y=65    return status returns
 On exit:
   if X=Y=0 then the ROM is fitted but disabled
   X=b0..5 current dot dash pattern repeat length (0 means 64)
     b6    if set flood fill is turned on
     b7    if set GXR ROM is turned on
   Y=number of pages allocated to sprites
 On entry:
   Y=66    return info on currently selected sprite
 On exit:
   if X=Y=0 then the ROM is fitted but disabled, or no sprite is selected
   X=pixel width 
   Y=pixel height

If the GXR ROM is absent, the call returns X=&FF and Y preserved. A call to OSBYTE &A3,242,65 can determine if GSX is absent, present but disabled, or present and enabled:

 On entry: A=&A3, X=242, Y=65
 On exit:  Y=65 - GSX ROM absent (Y preserved if ROM is absent)
           Y<64 - GSX ROM is present (not possible to have more
                  than 64 pages of workspace)
                  X.b7=0 - GSX ROM disabled
                  X.b7=1 - GSX ROM enabled

X=&F3 (243) 65Tube emulator

 On entry:
   Y=4     find code address
 On exit:
   if Y<>0, XY=address to jump to
   Called on Tube reset, *BASIC and NMIs to ask for any code entry address.
 On entry:
   Y=6     find *command to execute
 On exit:
   if Y<>0, XY=>*command to execute
   Called on Tube reset to ask for any startup command.

X=&FD (253) Cause a Reset

 On entry:
   Y=OSBYTE &FD reset type:
     0 = Soft Reset (Break)
     1 = Power-On Reset
     2 = Hard Reset (Ctrl-Break)
 On exit:
   Will only exit if the call is not implemented.
 
 Implemented by RSTROM and other ROMs.
 See also Reset from software.

X=&FE (254) Unknown

 This call is checked for by 65Tube.
 On entry:
   Y=unknown
 On exit:
   On 65Tube, X and Y returned preserved.

X=&FF (255) Acornsoft View family workspace flag

 On entry:
   Y<&80   read ROM's workspace byte at &DF0+romnum
   Y>&7F   set bit 7 of ROM's workspace byte at &DF0+romnum
   
   Y=&01/&81 read/set View's ROM workspace byte
   Y=&02/&82 read/set ViewSheet's ROM workspace byte
   Y=&03/&83 read/set ViewStore's ROM workspace byte
   Y=&04/&84 read/set ViewSpell's ROM workspace byte
 On exit:
   X=undefined (preserved)
   Y=ROM's workspace byte at &DF0+romnum
   
   Some versions of ViewSheet and ViewSpell do not implement the
   call to set the workspace byte. On 65Tube, X and Y are returned
   preserved, indicating the ROMs are not present.

The View family ROMs set their workspace byte to zero on reset, so this call normally returns &00 or &80. This allows callers to find if the View ROMs are present and perform actions such as calling them with their *Command without the risk of the command not being recognised and causing a disk access and a Bad command error.

The following code demonstrates using the calls.

  10 A%=163:X%=255
  20 FOR Y%=1 TO 4
  30   U%=((USR&FFF4)AND&FF0000)DIV65536
  40   READ A$:PRINT A$;" ";
  50   IF U%<>Y% THEN PRINT "present" ELSE PRINT "absent"
  60 NEXT Y%
  70 DATA VIEW,ViewSheet,ViewStore,ViewSpell

  A%=163:X%=255:Y%=1:IF ((USR&FFF4)AND&FF0000)DIV65536<>1 THEN *WORD

See Also

• http://mdfs.net/Docs/Comp/BBC/Osbyte80
• Reset from software

Jgharston 22:16, 26 May 2009 (UTC) Jgharston (talk) 02:26, 24 November 2020 (CET) Jgharston (talk) 00:24, 24 November 2022 (CET)