Difference between revisions of "OSBYTE &14"
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[[Category:OSBYTE]] | [[Category:OSBYTE]] | ||
| − | OSBYTE &14 (20) - Explode/implode user defined character font RAM | + | 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=0: characters &80 to &9F only are redefineable (default without Tube) | ||
X=1: characters &A0 to &BF are also redefineable | X=1: characters &A0 to &BF are also redefineable | ||
| Line 11: | Line 9: | ||
X=5: characters &40 to &5F are also redefineable | X=5: characters &40 to &5F are also redefineable | ||
X=6: characters &60 to &7F are also redefineable (default with Tube) | X=6: characters &60 to &7F are also redefineable (default with Tube) | ||
| + | On exit: | ||
| + | X=&00: font permantly exploded (MOS 3 and later) | ||
| + | X=&FF: font explodable/implodable (before MOS 3, ie Electron, BBC, BBC B+) | ||
| + | Y=&00: font permantly exploded (MOS 3 and later) | ||
| + | Y<>&00: new value OSHWM (not returned across Tube) | ||
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 below host OSHWM, allowing more characters to be defined. | 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 below host OSHWM, allowing more characters to be defined. | ||
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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. | 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== | ==See Also== | ||
| + | * [[OSBYTE &19]] reset font | ||
* http://mdfs.net/Docs/Comp/BBC/Osbyte00 | * http://mdfs.net/Docs/Comp/BBC/Osbyte00 | ||
| + | [[User:Jgharston|Jgharston]] ([[User talk:Jgharston|talk]]) 14:13, 31 August 2015 (UTC) | ||
[[User:Jgharston|Jgharston]] 21:30, 26 May 2009 (UTC)<br> | [[User:Jgharston|Jgharston]] 21:30, 26 May 2009 (UTC)<br> | ||
[[User:KJBracey|KJBracey]] 15:04, 5 December 2009 (UTC) | [[User:KJBracey|KJBracey]] 15:04, 5 December 2009 (UTC) | ||
Revision as of 15:13, 31 August 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 &A0 to &BF are also redefineable X=2: characters &C0 to &DF are also redefineable X=3: characters &E0 to &FF are also redefineable X=4: characters &20 to &3F are also redefineable X=5: characters &40 to &5F are also redefineable X=6: characters &60 to &7F are also redefineable (default with Tube) On exit: X=&00: font permantly exploded (MOS 3 and later) X=&FF: font explodable/implodable (before MOS 3, ie Electron, BBC, BBC B+) Y=&00: font permantly exploded (MOS 3 and later) Y<>&00: new value OSHWM (not returned across Tube)
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 below 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)
