hellomike wrote: ↑Thu 14 Sep 2023, 10:39
I'm not sure if this is intended functionality
It is, it's 'by design'. As you guessed, one specific use is to enable the UTF-8 character set in MODE 7. Exactly that combination is used by the
Ceefax.bbc example program, here's a snippet of the code:
Code: Select all
REM Select a 'teletext' video mode with support for UTF-8 pound sign:
VDU 23,22,640;500;16,20,16,128+8
MODE 7 : OFF
(no, I don't know why the 128 is there either, it's superfluous).
The teletext mode however seems to lose its block graphics.
Not necessarily, it depends on how you create them. For example this code works and draws a red box whilst the UTF-8 character set is active (make sure Unicode is enabled in the IDE):
Code: Select all
VDU 23, 22, 8; 8; 8, 8, 8, 8, 22, 7
PRINT "A red box:"CHR$27;CHR$145;CHR$27;CHR$247;CHR$27;CHR$251
PRINT "Some UTF-8 pound signs £££££"
If you look at
Ceefax.bbc you will see that all teletext control codes are preceded by a CHR$27 so that they will not interfere with the UTF-8 character encoding. You can always do that of course, but in regular MODE 7 it's optional whereas in UTF-8 mode it's mandatory.