Difference between revisions of "OSBYTE &14"
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On entry: | On entry: | ||
X=0: characters &80 to &9F only are redefineable (default without Tube) | X=0: characters &80 to &9F only are redefineable (default without Tube) | ||
| − | X=1: characters & | + | X=1: characters &80 to &BF are redefineable |
| − | X=2: characters & | + | X=2: characters &80 to &DF are redefineable |
| − | X=3: characters & | + | X=3: characters &80 to &FF are redefineable |
| − | X=4: characters &20 to &3F are | + | X=4: characters &20 to &3F, &80 to &FF are redefineable |
| − | X=5: characters & | + | X=5: characters &20 to &5F, &80 to &FF are redefineable |
| − | X=6: characters & | + | X=6: characters &20 to &FF are redefineable (default with Tube) |
On exit: | On exit: | ||
| − | X=&00: font | + | X=&00: font permanently exploded (MOS 3 and later) |
X=&FF: font explodable/implodable (before MOS 3, ie Electron, BBC, BBC B+) | X=&FF: font explodable/implodable (before MOS 3, ie Electron, BBC, BBC B+) | ||
| − | Y=&00: font | + | Y=&00: font permanently exploded (MOS 3 and later) |
Y<>&00: new value OSHWM (not returned across Tube) | Y<>&00: new value OSHWM (not returned across Tube) | ||
| + | |||
| + | BBC: X=return value from Service Call &11, &FF if call unclaimed, Y=new OSHWM | ||
| + | Master: X=&00, Y=0 | ||
| + | RISC OS: X=&01 (first font bank reset), Y=&03 (number of banks reset) | ||
| + | BB4W: X=&20 (character under cursor), Y=&00 | ||
| − | In the "imploded" state (X=0) only characters &80-&9F can be redefined with [[VDU 23]], as only 256 bytes is permanently allocated for font definition by the MOS. Other values of X "explode" the RAM and allocate 1 to 6 pages of font RAM | + | In the "imploded" state (X=0) only characters &80-&9F can be redefined with [[VDU 23]], as only 256 bytes is permanently allocated for font definition by the MOS. Other values of X "explode" the RAM and allocate 1 to 6 pages of font RAM pushing up host OSHWM, allowing more characters to be defined. |
This OSBYTE must be used with care within a language, as it can reduce the language's memory allocation. [[Paged_ROM_service_calls|Service call &11]] is issued to notify ROMs of the change in OSHWM. BASIC does not respond to this, so the *BASIC command should be issued to get it to reset PAGE. | This OSBYTE must be used with care within a language, as it can reduce the language's memory allocation. [[Paged_ROM_service_calls|Service call &11]] is issued to notify ROMs of the change in OSHWM. BASIC does not respond to this, so the *BASIC command should be issued to get it to reset PAGE. | ||
Revision as of 08:54, 6 September 2015
OSBYTE &14 (20) - Explode/implode user defined character font RAM and reset font On entry: X=0: characters &80 to &9F only are redefineable (default without Tube) X=1: characters &80 to &BF are redefineable X=2: characters &80 to &DF are redefineable X=3: characters &80 to &FF are redefineable X=4: characters &20 to &3F, &80 to &FF are redefineable X=5: characters &20 to &5F, &80 to &FF are redefineable X=6: characters &20 to &FF are redefineable (default with Tube) On exit: X=&00: font permanently exploded (MOS 3 and later) X=&FF: font explodable/implodable (before MOS 3, ie Electron, BBC, BBC B+) Y=&00: font permanently exploded (MOS 3 and later) Y<>&00: new value OSHWM (not returned across Tube) BBC: X=return value from Service Call &11, &FF if call unclaimed, Y=new OSHWM Master: X=&00, Y=0 RISC OS: X=&01 (first font bank reset), Y=&03 (number of banks reset) BB4W: X=&20 (character under cursor), Y=&00
In the "imploded" state (X=0) only characters &80-&9F can be redefined with VDU 23, as only 256 bytes is permanently allocated for font definition by the MOS. Other values of X "explode" the RAM and allocate 1 to 6 pages of font RAM pushing up host OSHWM, allowing more characters to be defined.
This OSBYTE must be used with care within a language, as it can reduce the language's memory allocation. Service call &11 is issued to notify ROMs of the change in OSHWM. BASIC does not respond to this, so the *BASIC command should be issued to get it to reset PAGE.
If unexploded, characters &20-&7F are taken from the ROM, and characters &A0-&FF are duplicates of &80-&9F.
When a Tube coprocessor is fitted, the font is fully exploded by default, as this does not take up language memory, but it can be imploded if desired.
OSBYTE &14 with any value of X also resets characters &20-&7F to the ROM font. Characters &80-&FF are not altered, contrary to some manuals.
MOS 3 and later ignores the input value of X. The font is always fully exploded, and the definitions do not take up user memory. The only effect of OSBYTE &14 is to reset characters &20-&7F. Characters &80-&FF are not altered, contrary to some manuals. To reset all characters, OSBYTE &19 should be used.
You should not examine the returned Y value, as OSBYTE calls <128 are defined to only return information in the X register, and only the X register is returned to the user in some environments (such as across the Tube).
See Also
- OSBYTE &19 reset font
- http://mdfs.net/Docs/Comp/BBC/Osbyte00
Jgharston (talk) 14:13, 31 August 2015 (UTC)
Jgharston 21:30, 26 May 2009 (UTC)
KJBracey 15:04, 5 December 2009 (UTC)
