Ceefax Engineering Test Page - BeebEm 4.13 & B-em

want to talk about MESS/model b/beebem/b-em/electrem/elkulator? do it here!
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Richard Russell
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Re: Ceefax Engineering Test Page - BeebEm 4.13 & B-em

Post by Richard Russell » Sat Nov 26, 2016 11:01 am

guesser wrote:If you are playing with editing teletext stuff you may want to look at a dedicated teletext editor as they have options to show visible control codes
I feel obliged to draw attention to the teletext editor in my Test Card Generator software, not least because it is itself written in BBC BASIC! It will display the control codes as symbols (abbreviations), and includes a simple 'sixel' graphics editor. I also have a standalone teletext editor based on that program but it's not currently available for download.

As far as test and demo pages are concerned, there is a carousel of quite a lot of them (mostly downloaded from Prestel) supplied with BBC BASIC for Windows (including the free trial version) as MODE7DEM.CAR in the EXAMPLES\GENERAL folder. It's also supplied with the cross-platform (Win32 / Linux-86 / MacOS / Android-86) versions of BBC BASIC.

I can confirm what other people have said, that you should not confuse MODE 7 with the official Videotex/Teletext specification. Specifically, any row containing double-height characters is sent only as one 40-character packet; what appears in the 'bottom half' is automatically determined by the decoder.

This has an interesting consequence: you can create a page containing double-height text which will instantly 'flip' to an entirely different content just by changing the very first character on the very first row! This happens because if every row contains a double-height control character only the even-numbered rows (0, 2, 4, 6 etc.) are visible: the odd numbered rows don't contribute to the display at all. If you then overwrite the double-height code in the top row, only the top row and the subsequent odd-numbered rows (1,3,5...) are visible. This is a tough test for a software-based Videotex/Teletext display.

Richard.

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jgharston
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Re: Ceefax Engineering Test Page - BeebEm 4.13 & B-em

Post by jgharston » Sat Nov 26, 2016 5:01 pm

I'll have to plug my teletext editor as well, which was my first significant program I wrote, and I originally wrote it so that I could display the teletext engineering page!
ABZTtxt

I've been meaning to tweek it so it runs correctly on Windows.

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.25
(C) Copyright J.G.Harston 1989,2005-2015
>_

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PitfallJones
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Re: Ceefax Engineering Test Page - BeebEm 4.13 & B-em

Post by PitfallJones » Wed Feb 22, 2017 3:16 pm

Do you have a .ssd of your program ABZTtxt?
Thanks
PJ

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jgharston
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Re: Ceefax Engineering Test Page - BeebEm 4.13 & B-em

Post by jgharston » Wed Feb 22, 2017 6:14 pm

PitfallJones wrote:Do you have a .ssd of your program ABZTtxt?
http://mdfs.net/Mirror/Image/JGH

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.25
(C) Copyright J.G.Harston 1989,2005-2015
>_

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PitfallJones
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Re: Ceefax Engineering Test Page - BeebEm 4.13 & B-em

Post by PitfallJones » Sat Feb 25, 2017 3:57 am

Thanks - that's great!
PJ

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Re: Ceefax Engineering Test Page - BeebEm 4.13 & B-em

Post by Soruk » Mon Jul 09, 2018 10:57 am

Just popping my head above the parapet here to say this thread has been a very useful resource in my attempt to make a reasonable emulation of Teletext work in Brandy BASIC V, along with a few Risc OS 5 extensions controlled via VDU23,18 as documented by BeebWiki. If anyone is interested I've put it up at http://brandy.matrixnetwork.co.uk/ - while its performance isn't great it correctly renders the Engineering page, including Reveal.

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Re: Ceefax Engineering Test Page - BeebEm 4.13 & B-em

Post by Coeus » Mon Jul 09, 2018 6:34 pm

Soruk wrote:
Mon Jul 09, 2018 10:57 am
Just popping my head above the parapet here to say this thread has been a very useful resource in my attempt to make a reasonable emulation of Teletext work in Brandy BASIC V, along with a few Risc OS 5 extensions controlled via VDU23,18 as documented by BeebWiki. If anyone is interested I've put it up at http://brandy.matrixnetwork.co.uk/ - while its performance isn't great it correctly renders the Engineering page, including Reveal.
Thanks for reminding me of Brandy BASIC. See viewtopic.php?f=54&t=15352

There is also something weird going on with executing the CLOCKSP timing program. On B-Em this executes in 49s and claims B-Em's speed is 1.97Mhz compared to a 2Mhz BBC B. Running this under Brandy BASIC it takes 1m22s, i.e. slower, and yet claims to be going much, much faster:
Screenshot from 2018-07-09 19-33-46.png
whereas if I run a Mandelbrot program written in BASIC, once having patched Brandy for the FOR loops (see above) it completes in 3s. In B-Em it has barely managed a few lines in 30s.
Last edited by Coeus on Mon Jul 09, 2018 6:41 pm, edited 1 time in total.

dp11
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Re: Ceefax Engineering Test Page - BeebEm 4.13 & B-em

Post by dp11 » Mon Jul 09, 2018 6:46 pm

Clocksp adjust its run time so that very fast cpus don't finish so quickly you end up with a test taking zero time.

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