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Looking for Acorn Electron help

Hi there,

Today I updated my Retro-X tool to convert PC images also to Acorn 
Electron. Unfortunaly I do not have this machine and only know which 
colours and display modes it got, by reading the instruction. My only 
retro machines I have are the Sinclair ZX Spectrum, SAM Coup� and Atari 
800 XL.
I need: some example screens for Acorn Electron in emulator format (Is 
there a standard screen format?), to make a viewer available in my program.
If exists: Viewer or converter for this retro format.
The same about other Acorn 8-Bit machines, if they have different 
graphical abilitys.

Thank you...

LCD
0
LCD
8/17/2008 5:25:24 PM
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On 17 Aug 2008 LCD <retrozx@[nospam]gmail.com> wrote:
> Today I updated my Retro-X tool to convert PC images also to Acorn
> Electron. Unfortunaly I do not have this machine and only know which
> colours and display modes it got,

The Electron supported all the modes that the BBC B had, except for 
Teletext mode. They are exactly the same format as the Beeb.

> The same about other Acorn 8-Bit machines, if they have different
> graphical abilitys.

If you'd like some screen dumps in various modes from a BBC, or BBC 
emulator, I'm sure someone here can provide them. But you'd be better
off reading the documentation on the format, as the byte to raster 
ordering is far from intuitive (well these days, it was perfectly
logical back then).

---druck

-- 
The ARM Club Free Software - http://www.armclub.org.uk/free/
The 32bit Conversions Page - http://www.quantumsoft.co.uk/druck/
0
news5843 (7461)
8/17/2008 10:00:36 PM
druck schrieb:
> On 17 Aug 2008 LCD <retrozx@[nospam]gmail.com> wrote:
>> Today I updated my Retro-X tool to convert PC images also to Acorn
>> Electron. Unfortunaly I do not have this machine and only know which
>> colours and display modes it got,
> 
> The Electron supported all the modes that the BBC B had, except for 
> Teletext mode. They are exactly the same format as the Beeb.
> 

Excellent! this means modes 0-6. AFAIK Mode 7 is the teletext mode. For 
the teletext mode: Does it use 8x8 chars or 8x16 (as the documentation 
said: Interlace bit is set)?

>> The same about other Acorn 8-Bit machines, if they have different
>> graphical abilitys.
> 
> If you'd like some screen dumps in various modes from a BBC, or BBC 
> emulator, I'm sure someone here can provide them. But you'd be better
> off reading the documentation on the format, as the byte to raster 
> ordering is far from intuitive (well these days, it was perfectly
> logical back then).
> 
Oh, believe me, I have decoded some more complicated byte orders like 
that from Sinclair QL or Amstrad CPC for inclusion in my converter (some 
of them by reverse engineering). The Sinclair QL for example has the 
most complicated binary layout. I saw the binary layout of colour 
encoding from Acorn Electron in the technical manual, and it is not too 
complex. Anything can be easy decoded with binary operartions like bit 
shifting and binary AND and OR, but I want to test anything I do with 
existing files to make sure, anything will work okay.
I also do not know how the Palette is stored in the screen files, but 
that is very important.
Is there a Acorn 8 Bit - screen editor for windows PCs? I googled a bit 
but have not found anything.

LCD
0
LCD
8/18/2008 6:42:02 AM
LCD <retrozx@[nospam]gmail.com> wrote:
> Excellent! this means modes 0-6. AFAIK Mode 7 is the teletext mode. For 
> the teletext mode: Does it use 8x8 chars or 8x16 (as the documentation 
> said: Interlace bit is set)?

7x5 (it was all generated by the SAA5050 teletext chip which drove the
raster directly), I would assume interlaced.  A 'screendump' of a teletext
mode is a 1K file containing the text and control codes - you need a
teletext emulator to convert that to a bitmap.

> I also do not know how the Palette is stored in the screen files, but 
> that is very important.

There isn't one (IIRC).  Screendumps were just a snapshot of screen memory -
the palette was somewhere else.  You had to program the palette separately
if you wanted to change the colours - but I bet that the majority of
screendumps use the default colours.

> Is there a Acorn 8 Bit - screen editor for windows PCs? I googled a bit 
> but have not found anything.

I don't think so.  There might be a BBC screen editor you could run on an
emulator.

Theo
0
news539 (2440)
8/18/2008 11:35:03 AM
Theo Markettos schrieb:
> LCD <retrozx@[nospam]gmail.com> wrote:
>> Excellent! this means modes 0-6. AFAIK Mode 7 is the teletext mode. For 
>> the teletext mode: Does it use 8x8 chars or 8x16 (as the documentation 
>> said: Interlace bit is set)?
> 
> 7x5 (it was all generated by the SAA5050 teletext chip which drove the
> raster directly), I would assume interlaced.  A 'screendump' of a teletext
> mode is a 1K file containing the text and control codes - you need a
> teletext emulator to convert that to a bitmap.
> 
Okay, the idea was co convert pictures to the teletext mode, but after 
my converter can only work with 8x1 to 8x16 blocks, this won't work (Or 
maybe I will write new routines to handle this conversion).
>> I also do not know how the Palette is stored in the screen files, but 
>> that is very important.
> 
> There isn't one (IIRC).  Screendumps were just a snapshot of screen memory -
> the palette was somewhere else.  You had to program the palette separately
> if you wanted to change the colours - but I bet that the majority of
> screendumps use the default colours.
> 
Thats what I do with mode 2 (160x256 and 8 TTL RGB colours - no use for 
flashing). I should really use standard colours for 4-colour modes

>> Is there a Acorn 8 Bit - screen editor for windows PCs? I googled a bit 
>> but have not found anything.
> 
> I don't think so.  There might be a BBC screen editor you could run on an
> emulator.
> 
> Theo

Thank you very much, Theo.

LCD
0
LCD
8/18/2008 4:26:58 PM
LCD <retrozx@[nospam]gmail.com> wrote:
> Theo Markettos schrieb:
> > 7x5 (it was all generated by the SAA5050 teletext chip which drove the
> > raster directly), I would assume interlaced.  A 'screendump' of a teletext
> > mode is a 1K file containing the text and control codes - you need a
> > teletext emulator to convert that to a bitmap.
> > 
> Okay, the idea was co convert pictures to the teletext mode, but after 
> my converter can only work with 8x1 to 8x16 blocks, this won't work (Or 
> maybe I will write new routines to handle this conversion).

If you don't mind your teletext mode looking slightly different, you can
always use an 8x8 or 8x16 font to display the text.  I think this is what
more modern TVs do.  Teletext is only 40x25 chars so you've got plenty of
pixels to play with.  I think RISC OS 2 and 3 use this technique too in
their teletext modes (certainly the font is a bit different from the
SAA5050's).

Theo
0
news539 (2440)
8/18/2008 9:37:40 PM
Theo Markettos schrieb:
> LCD <retrozx@[nospam]gmail.com> wrote:
>> Theo Markettos schrieb:
>>> 7x5 (it was all generated by the SAA5050 teletext chip which drove the
>>> raster directly), I would assume interlaced.  A 'screendump' of a teletext
>>> mode is a 1K file containing the text and control codes - you need a
>>> teletext emulator to convert that to a bitmap.
>>>
>> Okay, the idea was co convert pictures to the teletext mode, but after 
>> my converter can only work with 8x1 to 8x16 blocks, this won't work (Or 
>> maybe I will write new routines to handle this conversion).
> 
> If you don't mind your teletext mode looking slightly different, you can
> always use an 8x8 or 8x16 font to display the text.  I think this is what
> more modern TVs do.  Teletext is only 40x25 chars so you've got plenty of
> pixels to play with.  I think RISC OS 2 and 3 use this technique too in
> their teletext modes (certainly the font is a bit different from the
> SAA5050's).
> 
> Theo

40x25 Characters sounds very good, but how does it occupy 1 KB? is it 
without colours?. I was looking for binary import/export in Beeb, but 
not found anything like that, but it would be very important to test the 
conversion. I should also check how to POKE the memory in BBC Basic to 
video memory, because it looks like it works very different from my 
other machines.
At moment I have written following conversion modes:
Mode 0 640x256 Monochrome (Solid, Midtone, Ordered dither, error 
diffusions, random and 3x3 clusters)
Mode 2 160x256 8 Colours (Solid, Midtone, Ordered dither, Error Diffusions)
Mode 2 160x256 GreyTV Mode 8 Grey Levels (Solid, Midtone, Ordered 
Dither, Error diffusions), just need to switch colours off on the 
monitor for photographics quality.
Mode 4 320x256 Monochrome (Solid, Midtone, Ordered dither, Error 
diffusions, Random and 3x3 Clusters)
The conversion is done in Real-time with multiple trackbars to control 
the dithering process.

LCD
0
LCD
8/18/2008 11:30:24 PM
In article <6fe42$48aa0610$557f5a28$12455@news.inode.at>,
   LCD <retrozx@[nospam]gmail.com> wrote:
> Theo Markettos schrieb:

[The Beeb's Teletext Mode 7]

> 40x25 Characters sounds very good, but how does it occupy 1 KB? is
> it without colours?.

It has 8 colours (black red green blue yellow cyan magenta white),
plus 8 flashing combinations.

The colours (and some other effects, such as double height
characters) are represented by using up a character space with a
'control' character which tells the display system the colour (or
other effect) of whatever follows it on the line (and which itself
appears as just a space on the screen)

For more specific details of the various control codes, you'll have
to either use Google or hope someone will be able to reply to this
pointing you to a reference.

-- 
VinceH
0
spam5752 (1717)
8/19/2008 7:59:26 AM
VinceH wrote:
> > 40x25 Characters sounds very good, but how does it occupy 1 KB? is
> > it without colours?.
> It has 8 colours (black red green blue yellow cyan magenta white),
> plus 8 flashing combinations.

A teletext display consists of 25 lines of 40 7-bit characters.
The eigth bit is ignored. Each character can either be a displayable
character in the range &20 to &7F (or &A0 to &FF) or a control
character in the range &00 to &1F (or &80 to &9F). You will find
that BBC MODE 7 displays usually use the range &20 to &9F, ie b7
clear for displayable characters and b7 set for control characters.

Control characters take up a character cell on the screen, and are
usually displayed as a space.

Each line starts in a defined state, this being:
black background, white foreground, text, nonflashing, single height,
contiguous (joined) graphics.

Control characters change the state of the /following/ characters
on the same line. Control characters are:

&00/&80 - NULL
&01/&81 - Red alphanumeric
&02/&82 - Green alphanumeric
&03/&83 - Yellow alphanumeric
&04/&84 - Blue alphanumeric
&05/&85 - Magenta alphanumeric
&06/&86 - Cyan alphanumeric
&07/&87 - White alphanumeric
&08/&88 - Flash
&09/&89 - Steady
&0A/&9A - End Box
&0B/&9B - Start Box
&0C/&8C - Normal height
&0D/&8D - Double height
&0E/&8E - SO (NULL)
&0F/&8F - SI (NULL)
&10/&90 - DLE (NULL)
&11/&91 - Red graphics
&12/&92 - Green graphics
&13/&93 - Yellow graphics
&14/&94 - Blue graphics
&15/&95 - Magenta graphics
&16/&96 - Cyan graphics
&17/&97 - White graphics
&18/&98 - Conceal
&19/&99 - Contiguous graphics
&1A/&9A - Seperated graphics
&1B/&9B - Black background
&1C/&9C - New background - new background colour is current foreground
colour
&1D/&9D - ESC (NULL)
&1E/&9E - Hold graphics - last displayed graphics character is
displayed
instead of a space in a character cell occupied by a control code
&1F/&9F - Release graphics

After a alphanumeric colour code, all displayable characters are
displayed in the current background colour and the specified
foreground colour. After a graphics colour code, all upper case
letters are displayed, and other displayable characters are
displayed as a 6-pixel graphics character (see RTR later).

The =A3, #, _ characters are swapped around in the teletext character
set, so a memory dump will have &23 for =A3, &60 for _ and &5F for #.

The BBC Micro User Guide has a bitmap diagram of the teletext
character set in one of the appendixes.

To edit a teletext screen, you could try ABZTTxt at
<http://mdfs.net/System/Teletext/>, works on any system
capable of running BBC BASIC and with MODE 7 (BBC, Master,
RISC OS, Windows.....)

See also http://www.rtrussell.co.uk/bbcwin/manual/bbcwinh.html

--
JGH
0
jgh2 (975)
8/19/2008 9:30:37 AM
jgharston schrieb:
> VinceH wrote:
>>> 40x25 Characters sounds very good, but how does it occupy 1 KB? is
>>> it without colours?.
>> It has 8 colours (black red green blue yellow cyan magenta white),
>> plus 8 flashing combinations.
> 
> A teletext display consists of 25 lines of 40 7-bit characters.
> The eigth bit is ignored. Each character can either be a displayable
> character in the range &20 to &7F (or &A0 to &FF) or a control
> character in the range &00 to &1F (or &80 to &9F). You will find
> that BBC MODE 7 displays usually use the range &20 to &9F, ie b7
> clear for displayable characters and b7 set for control characters.
> 
> Control characters take up a character cell on the screen, and are
> usually displayed as a space.
> 
> Each line starts in a defined state, this being:
> black background, white foreground, text, nonflashing, single height,
> contiguous (joined) graphics.
> 
> Control characters change the state of the /following/ characters
> on the same line. Control characters are:
> 
> &00/&80 - NULL
> &01/&81 - Red alphanumeric
> &02/&82 - Green alphanumeric
> &03/&83 - Yellow alphanumeric
> &04/&84 - Blue alphanumeric
> &05/&85 - Magenta alphanumeric
> &06/&86 - Cyan alphanumeric
> &07/&87 - White alphanumeric
> &08/&88 - Flash
> &09/&89 - Steady
> &0A/&9A - End Box
> &0B/&9B - Start Box
> &0C/&8C - Normal height
> &0D/&8D - Double height
> &0E/&8E - SO (NULL)
> &0F/&8F - SI (NULL)
> &10/&90 - DLE (NULL)
> &11/&91 - Red graphics
> &12/&92 - Green graphics
> &13/&93 - Yellow graphics
> &14/&94 - Blue graphics
> &15/&95 - Magenta graphics
> &16/&96 - Cyan graphics
> &17/&97 - White graphics
> &18/&98 - Conceal
> &19/&99 - Contiguous graphics
> &1A/&9A - Seperated graphics
> &1B/&9B - Black background
> &1C/&9C - New background - new background colour is current foreground
> colour
> &1D/&9D - ESC (NULL)
> &1E/&9E - Hold graphics - last displayed graphics character is
> displayed
> instead of a space in a character cell occupied by a control code
> &1F/&9F - Release graphics
> 
> After a alphanumeric colour code, all displayable characters are
> displayed in the current background colour and the specified
> foreground colour. After a graphics colour code, all upper case
> letters are displayed, and other displayable characters are
> displayed as a 6-pixel graphics character (see RTR later).
> 
> The �, #, _ characters are swapped around in the teletext character
> set, so a memory dump will have &23 for �, &60 for _ and &5F for #.
> 
> The BBC Micro User Guide has a bitmap diagram of the teletext
> character set in one of the appendixes.
> 
> To edit a teletext screen, you could try ABZTTxt at
> <http://mdfs.net/System/Teletext/>, works on any system
> capable of running BBC BASIC and with MODE 7 (BBC, Master,
> RISC OS, Windows.....)
> 
> See also http://www.rtrussell.co.uk/bbcwin/manual/bbcwinh.html
> 
> --
> JGH

Okay, thank you very much! You are great! I think, this will help me a 
lot... I will download the manual as soon as possible!


LCD
0
LCD
8/19/2008 11:42:34 AM
On Aug 19, 12:30=A0am, LCD <retrozx@[nospam]gmail.com> wrote:
> 40x25 Characters sounds very good, but how does it occupy 1 KB?
> is it without colours?

The full Teletext specification is available here:

 http://www.doc.ic.ac.uk/~ih/teaching/teletext/tt-spec/spec.doc

Note that although the teletext character set is basically 7x5 (or 9x5
if you include descenders) the hardware implementation in the BBC
Micro (using the SAA5050 chip) performs 'character rounding' to give
effectively an 18x10 resolution.

The Teletext mode is also capable of double-height characters,
flashing characters and low-resolution graphics (both 'contiguous' and
'separated').  Emulating it accurately in software is monstrously
difficult, and I'm prepared to bet that the emulation in 'BBC BASIC
for Windows' is the only one that gets it completely right.

Richard.
http://www.rtrussell.co.uk/
To reply by email change 'news' to my forename.
0
news1075 (671)
8/19/2008 11:51:47 AM
Richard Russell schrieb:
> On Aug 19, 12:30 am, LCD <retrozx@[nospam]gmail.com> wrote:
>> 40x25 Characters sounds very good, but how does it occupy 1 KB?
>> is it without colours?
> 
> The full Teletext specification is available here:
> 
>  http://www.doc.ic.ac.uk/~ih/teaching/teletext/tt-spec/spec.doc
> 
> Note that although the teletext character set is basically 7x5 (or 9x5
> if you include descenders) the hardware implementation in the BBC
> Micro (using the SAA5050 chip) performs 'character rounding' to give
> effectively an 18x10 resolution.
> 
> The Teletext mode is also capable of double-height characters,
> flashing characters and low-resolution graphics (both 'contiguous' and
> 'separated').  Emulating it accurately in software is monstrously
> difficult, and I'm prepared to bet that the emulation in 'BBC BASIC
> for Windows' is the only one that gets it completely right.
> 
> Richard.
> http://www.rtrussell.co.uk/
> To reply by email change 'news' to my forename.

Excellent! Now I see how it works. So in Teletext mode if I convert 
graphics, the maximal resolution will be 80x75 "pixels". I thought it 
was 80x50.
This documentation is very technical, but it explains me some details.

Thank you for this.
If I will have more questions, I will ask there again...
By the way, a earlier version of my "Retro-X" converter is available on 
http://www.worldofspectrum.org in utility section (screen manipulation)
and I will upload the new version there too soon as possible.

LCD
0
LCD
8/20/2008 7:09:32 AM
druck schrieb:
> On 17 Aug 2008 LCD <retrozx@[nospam]gmail.com> wrote:
>> Today I updated my Retro-X tool to convert PC images also to Acorn
>> Electron. Unfortunaly I do not have this machine and only know which
>> colours and display modes it got,
> 
> The Electron supported all the modes that the BBC B had, except for 
> Teletext mode. They are exactly the same format as the Beeb.
> 
>> The same about other Acorn 8-Bit machines, if they have different
>> graphical abilitys.
> 
> If you'd like some screen dumps in various modes from a BBC, or BBC 
> emulator, I'm sure someone here can provide them. But you'd be better
> off reading the documentation on the format, as the byte to raster 
> ordering is far from intuitive (well these days, it was perfectly
> logical back then).
> 
> ---druck
> 
There is just one question left: How to load the binary data that my 
program creates, into Emulators like Beeb? Sim Coup� Emulator and many 
Spectrum emulators have a option to load a binary PC file into memory at 
selected memory location, but Beeb has not such a option, or is it hidden?

LCD
0
LCD
8/21/2008 1:47:36 PM
On Aug 21, 2:47=A0pm, LCD <retrozx@[nospam]gmail.com> wrote:
> Spectrum emulators have a option to load a binary PC file into
> memory at selected memory location, but Beeb has not such a option

Huh?

*LOAD filename hexaddress

OSCLI "LOAD "+filename$+" "+STR$~address%

Richard.
http://www.rtrussell.co.uk/
To reply by email change 'news' to my forename.
0
news1075 (671)
8/21/2008 3:57:40 PM
Richard Russell schrieb:
> On Aug 21, 2:47 pm, LCD <retrozx@[nospam]gmail.com> wrote:
>> Spectrum emulators have a option to load a binary PC file into
>> memory at selected memory location, but Beeb has not such a option
> 
> Huh?
> 
> *LOAD filename hexaddress
> 
> OSCLI "LOAD "+filename$+" "+STR$~address%
> 
> Richard.
> http://www.rtrussell.co.uk/
> To reply by email change 'news' to my forename.

Was this not for loading files from containers (tape/disc images) only? 
I never successed loading a binary PC file this way, but maybe I'm too 
inexperienced using Beeb emulator.

LCD
0
LCD
8/21/2008 10:34:43 PM
On Aug 21, 11:34=A0pm, LCD <retrozx@[nospam]gmail.com> wrote:
> Was this not for loading files from containers (tape/disc images) only?

You may well be right; I have no experience of Beeb emulators.

Richard.
http://www.rtrussell.co.uk/
To reply by email change 'news' to my forename.
0
news1075 (671)
8/22/2008 4:02:24 PM
On 2008-08-19, Richard Russell <news@rtrussell.co.uk> wrote:
> 'separated').  Emulating it accurately in software is monstrously
> difficult, and I'm prepared to bet that the emulation in 'BBC BASIC
> for Windows' is the only one that gets it completely right.

'Monstrously difficult' seems to overstate the problem - I bet many
modern TVs do it in software, and back in the day, the Sinclair Spectrum
did it just fine with the VTX-5000 modem for Prestel/Micronet (and
viewdata bulletin boards).

-- 
From the sunny Isle of Man.
Yes, the Reply-To email address is valid.
0
dylan1 (55)
8/29/2008 12:38:13 PM
On 19 Aug 2008 Richard Russell <news@rtrussell.co.uk> wrote:
> The Teletext mode is also capable of double-height characters,
> flashing characters and low-resolution graphics (both 'contiguous' and
> 'separated').  Emulating it accurately in software is monstrously
> difficult, and I'm prepared to bet that the emulation in 'BBC BASIC
> for Windows' is the only one that gets it completely right.

Rubbish! Richard Granville's Telext emulation module as used in his 
Octopus Teletext provides a prefect emulation as far as I can tell.
I use it, (with kind permission) in my Graphic TaskWindows to provide 
Mode 7 compatibility (1st link below).

---druck

-- 
The ARM Club Free Software - http://www.armclub.org.uk/free/
The 32bit Conversions Page - http://www.quantumsoft.co.uk/druck/
0
news5843 (7461)
8/29/2008 9:53:20 PM
On Aug 29, 1:38=A0pm, Dylan Smith <dy...@vexed3.alioth.net> wrote:
> 'Monstrously difficult' seems to overstate the problem

I stand by my claim.  The MODE 7 emulation was one of the most
difficult parts of BBC BASIC for Windows, despite having previously
written the MODE 7 emulator for MS-DOS BBC BASIC (86) - which turned
out to have several flaws when stressed.

> - I bet many modern TVs do it in software

Software?  Unlikely.  Firmware, yes, but of course that's exactly how
the Viewdata display standard was designed: to suit a hardware/
firmware implementation.

> and back in the day, the Sinclair Spectrum
> did it just fine with the VTX-5000 modem for Prestel/Micronet (and
> viewdata bulletin boards).

Just fine?  I'm willing to bet it had faults.  But in any case MODE 7
is *not* the same as Teletext/Viewdata.  With Teletext/Viewdata you
know the data will arrive in 'display order', that is the characters
on a line (row) will be stored in the order in which they appear (left
to right).  That makes the emulation much more straightforward.

With MODE 7 you have 'random access' to the display, e.g. using
TAB(x,y).  The most challenging problems I had to face with my MODE 7
software emulation were to make it work correctly when characters were
stored 'out of sequence'.  I have two BBC BASIC test programs:
MODE7REV and MODE7RND which store the characters in reverse order and
in random order respectively.  If you know of a software emulation of
MODE 7, other than mine, I'd be extremely interested to see what it
makes of those!

Richard.
http://www.rtrussell.co.uk/
To reply by email change 'news' to my forename.
0
news1075 (671)
8/29/2008 10:16:43 PM
On 29 Aug 2008 Richard Russell <news@rtrussell.co.uk> wrote:
> With MODE 7 you have 'random access' to the display, e.g. using
> TAB(x,y).  The most challenging problems I had to face with my MODE 7
> software emulation were to make it work correctly when characters were
> stored 'out of sequence'.  I have two BBC BASIC test programs:
> MODE7REV and MODE7RND which store the characters in reverse order and
> in random order respectively.  If you know of a software emulation of
> MODE 7, other than mine, I'd be extremely interested to see what it
> makes of those!

The teletext screen is generated just as the hardware chip does it, 
line by line top to bottom. Instead of on every frame, it can be done
just when anything is written to it. Software generating the bitmap 
from 1K of data, is a trivial task for any post-8bit system.

---druck

-- 
The ARM Club Free Software - http://www.armclub.org.uk/free/
The 32bit Conversions Page - http://www.quantumsoft.co.uk/druck/
0
news5843 (7461)
8/31/2008 3:22:10 PM
In article <8ff388d74f.druck@druck.freeuk.net>, druck
<news@druck.freeuk.com> wrote:
> The teletext screen is generated just as the hardware chip does it,
> line by line top to bottom. Instead of on every frame, it can be done
> just when anything is written to it. Software generating the bitmap
> from 1K of data, is a trivial task for any post-8bit system.

There is trivial for some and hard work for others.

I wrote a MODE 7 Epsom printer screen dump in 6502 assembler on the BBC
and found it hard work and anything but trivial for me. Maybe others
would have found it trivial?

-- 
Barry A.
To reply by email:- barry d o t allen a t talktalk d o t net
Replace the d o t and a t by the usual.
0
evanallen1 (351)
8/31/2008 3:49:54 PM
On 31 Aug 2008 "Barry Allen (news)" <evanallen@onetel.net.uk.invalid> 
wrote:

> In article <8ff388d74f.druck@druck.freeuk.net>, druck
> <news@druck.freeuk.com> wrote:
>> The teletext screen is generated just as the hardware chip does it,
>> line by line top to bottom. Instead of on every frame, it can be done
>> just when anything is written to it. Software generating the bitmap
>> from 1K of data, is a trivial task for any post-8bit system.

> There is trivial for some and hard work for others.

I'm refering to the computational effort of regenerating the entire 
teletext screen, compared to trying to compute the results of an 
arbitrary change in the input buffer, which is a lot more difficult.

> I wrote a MODE 7 Epsom printer screen dump in 6502 assembler on the BBC
> and found it hard work and anything but trivial for me. Maybe others
> would have found it trivial?

The idea behind telext is that it could be generated on the fly by low 
complexity chips using a very limited state machine. Follow that 
principle in a sofware implementation, and it shouldn't be too hard.

---druck

-- 
The ARM Club Free Software - http://www.armclub.org.uk/free/
The 32bit Conversions Page - http://www.quantumsoft.co.uk/druck/
0
news5843 (7461)
8/31/2008 4:13:57 PM
On Aug 31, 4:22=A0pm, druck <n...@druck.freeuk.com> wrote:
> The teletext screen is generated just as the hardware chip does it,
> line by line top to bottom. Instead of on every frame, it can be
> done just when anything is written to it. Software generating the
> bitmap from 1K of data, is a trivial task for any post-8bit system.

It's true that if you re-create the entire screen whenever anything
changes you can overcome difficulties associated with the order in
which characters are written.  However, on the Windows 95 PC on which
I developed 'BBC BASIC for Windows' that would have been unacceptably
slow, and even on a modern machine is likely to make MODE 7 the
slowest rather than the fastest MODE!

In BB4W only as much of the screen is updated as needs to be, which
may be (and frequently is) as little as one character, but may be as
much as everything from the start of the row containing the changed
character to the end of the screen (when a double-height change
'cascades' down the entire screen).

But I still contend that, even if you do rebuild the entire screen
every time, to get a Teletext/Viewdata emulation 100% right is far
from straightforward.  Many implementations, even some hardware ones,
get the 'set at' and 'set after' rules wrong (the difference only
being visible in 'held graphics' mode), and double-height is
notoriously difficult to get completely right.

Some TVs and dedicated Viewdata terminals had faults of that kind,
which is precisely why the test pages I supply with BB4W were
originally provided on Prestel and/or Ceefax to allow users to check
their own equipment (although those tests are far from comprehensive).

If the emulation you mention is 100% correct then I congratulate its
author, but it puts it into a very select class of both hardware and
software implementations of the Teletext/Viewdata standard.

Richard.
http://www.rtrussell.co.uk/
To reply by email change 'news' to my forename.

0
news1075 (671)
8/31/2008 5:23:20 PM
In article <4fd78b7d95evanallen@onetel.net.uk.invalid>, Barry Allen (news)
<URL:mailto:evanallen@onetel.net.uk.invalid> wrote:
> In article <8ff388d74f.druck@druck.freeuk.net>, druck
> <news@druck.freeuk.com> wrote:
> > The teletext screen is generated just as the hardware chip does it,
> > line by line top to bottom. Instead of on every frame, it can be done
> > just when anything is written to it. Software generating the bitmap
> > from 1K of data, is a trivial task for any post-8bit system.
> 
> There is trivial for some and hard work for others.
> 
> I wrote a MODE 7 Epsom printer screen dump in 6502 assembler on the BBC
> and found it hard work and anything but trivial for me. Maybe others
> would have found it trivial?

A bet the flashing colours were difficult to do ;-) 


Chris Evans

-- 
CJE Micro's / 4D                'RISC OS Specialists'
Telephone: 01903 523222             Fax: 01903 523679
chris@cjemicros.co.uk     http://www.cjemicros.co.uk/
78 Brighton Road, Worthing, West Sussex,     BN11 2EN
The most beautiful thing anyone can wear, is a smile!

0
chris8168 (2937)
9/1/2008 11:59:34 AM
In article <ant011134fc4pErr@client.cjemicros.co.uk>, Chris Evans
<chris@cjemicros.co.uk> wrote:
> In article <4fd78b7d95evanallen@onetel.net.uk.invalid>, Barry Allen
> (news) <URL:mailto:evanallen@onetel.net.uk.invalid> wrote:
> > There is trivial for some and hard work for others.
> > 
> > I wrote a MODE 7 Epsom printer screen dump in 6502 assembler on the
> > BBC and found it hard work and anything but trivial for me. Maybe
> > others would have found it trivial?

> A bet the flashing colours were difficult to do ;-) 

Nah! Trivial!

-- 
Barry A.
To reply by email:- barry d o t allen a t talktalk d o t net
Replace the d o t and a t by the usual.
0
evanallen1 (351)
9/1/2008 1:08:39 PM
"Barry Allen (news)" <evanallen@onetel.net.uk.invalid> writes:

> In article <ant011134fc4pErr@client.cjemicros.co.uk>, Chris Evans
> <chris@cjemicros.co.uk> wrote:
>> In article <4fd78b7d95evanallen@onetel.net.uk.invalid>, Barry Allen
>> (news) <URL:mailto:evanallen@onetel.net.uk.invalid> wrote:
>> > There is trivial for some and hard work for others.
>> > 
>> > I wrote a MODE 7 Epsom printer screen dump in 6502 assembler on the
>> > BBC and found it hard work and anything but trivial for me. Maybe
>> > others would have found it trivial?
>
>> A bet the flashing colours were difficult to do ;-) 
>
> Nah! Trivial!

	I'm guessing that you could use colour cycling for this, no?

	The main problem with emulated Teletext would probably be
memory use - Teletext mode uses only 1K, while a colour graphics mode
would use at least 8KB - and that would not even give you a full
colour palette.
0
raw1 (128)
9/1/2008 5:48:22 PM
In article <ant011134fc4pErr@client.cjemicros.co.uk>,
   Chris Evans <chris@cjemicros.co.uk> wrote:
> In article <4fd78b7d95evanallen@onetel.net.uk.invalid>, Barry Allen (news)
> <URL:mailto:evanallen@onetel.net.uk.invalid> wrote:
> > In article <8ff388d74f.druck@druck.freeuk.net>, druck
> > <news@druck.freeuk.com> wrote:
> > > The teletext screen is generated just as the hardware chip does it,
> > > line by line top to bottom. Instead of on every frame, it can be done
> > > just when anything is written to it. Software generating the bitmap
> > > from 1K of data, is a trivial task for any post-8bit system.
> > 
> > There is trivial for some and hard work for others.
> > 
> > I wrote a MODE 7 Epsom printer screen dump in 6502 assembler on the BBC
> > and found it hard work and anything but trivial for me. Maybe others
> > would have found it trivial?

> A bet the flashing colours were difficult to do ;-) 

Indeed so.  I once produced a Ceefax to printer program, and a complaint
came back that the printed version didn't flash.

-- 
From KT24 - in "Leafy Surrey"

Using a RISC OS computer running v5.11 

0
charles7889 (2007)
9/1/2008 7:58:24 PM
Reply: