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Old 6th Mar 2012, 11:48 am   #41
terrykc
Rest in Peace
 
Join Date: Nov 2010
Location: North Hykeham, Lincolnshire, UK.
Posts: 515
Default Re: IMOGen Test Card & Teletext Generator

Quote:
Originally Posted by Parabola View Post
... Sorry about the weather outlook. It took me about 6 hours to re-code that page back into 7 bit ascii from a .gif of the original and, to be honest, the actual forecast wasn't the highest priority in my mind ...
It's quite a coincidence that the forecast you 'brought back from the dead' bears a marked similarity to the weather we've been experiencing over the last few days!

Quote:
Originally Posted by Parabola View Post
IMOGen puts out 12 lines per field, so the page counter between page selections moves like a blur! I was a little concerned at first as to whether so many lines would be tolerated by such an early decoder as is in the G11 ...
All versions of the UK Teletext Specification (there were three) specified that all 16 available lines in the VBI could be used. Although the early TIfax decoder was designed before the 'new' features (background colour, double height, etc.) were added, it worked on all 16 lines.

I know what you mean about the page numbers - we used 14 lines for the test pages and bridged BBC1 CEEFAX onto the remaining two.

CEEFAX was used to create interest and demonstrate the capabilities of Teletext but, in reality, the primary purpose was to test the capability of a large, private, cable TV system by means of an error counter piggy-backed onto the TIfax decoder.

Quote:
Originally Posted by Parabola View Post
Quote:
Originally Posted by terrykc View Post
... rows can be transmitted in any order.
Well yes, as long as you keep a track of where your header rows are inserted. One out of sequence data line on the wrong side of a header row and it all goes to pot!
Agreed, but it wasn't a problem with the Philips generator as the row numbers were included in the data. It was simply a case of re-ordering the data before burning the PROM.
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