Tony Duell wrote:
>> I'm planning to build a video generator using a PIC and then connect
>> Sync to the Cub653, CVBS to the TTX board, then connect R.G.B. from
>> the TTX board to the monitor. In theory that *should* get me a
>> picture. I've got an I2C
> Should it? Why? The Teletext decoder is not also a colour video
> decoder (or at least the ones I am used to aren't). The RGB outputs
> of the Teletext decoder are mixed/multiplexed with the RGB outputs of
> a colour decoder and then fed to the video output stages.
Hmm... I thought it used the CVBS signal to lock onto and then generated RGB
video out. RGB -> Cub monitor, Sync from vidgen -> Cub monitor, CVBS from
vidgen -> TTX board.
Anyway, I'll see if my PICDREAM video generator can generate a good enough
signal for the TTX board to generate some form of video signal. The 5281
also seems to allow access to its RAM via I2C register accesses - set the X
and Y co-ords, then write a character to it.
Oh, how I wish I had a TX91G service manual so I could find out just how
this pesky thing works and what Thomson originally designed it to use... The
TX90 uses an SAA5281, the schematic I've got for the TTX board has had the
"SAA52" bit nipped off and most of the next digit. It looks like a 2-chip
design, though.
> Unless there's a valid teletext stream in the video signal, the
> teletext decoder is not going to produce any video....
*thud* *thud* *thud* *thud* <-- sound of philpem's head hitting the wall
many times...
> I know you have this teletext board using these unknown ICs, but
> really your life would be a lot simpler if you used the SAA5243 or
> one of its later replacements. Those can generate sync signals. Those
> can be used as just video display ICs (without needing a valid
> teletext input -- you can store data in the video RAM via the I2C
> bus). And there's a lot of documentation out there for them.
Know anyone that stocks the SAA5243? Can't find it on Farnell's site, nor
does my CPC catalogue list it.
>> interface for my laptop that still works, so I have some way of
>> controlling it.
>
> If your OS allows you to have direct access to the printer port I/O
> registers, you can make an I2C interface for the PC using 2 diodes
[snip]
Actually, mine uses a 7406 (IIRC) buffer. It's a clone of the original
Philips I2C probing pod. It looks like it can intercept I2C traffic and also
output it.
I'll see if I can persuade the TTX board to generate any video tonight. I've
got a Tek 466 storage scope and a Gould OS1100A in case I need an extra two
channels. Anyone know of a source for Tek 1x/10x probes? The 466 seems to
want the ring around the BNC connector shorting to the shield (GND) to push
it into 10x mode. Guess how many probes I've found that do that... That's
right, none.
Later.
--
Phil.
philpem_at_dsl.pipex.com
http://www.philpem.dsl.pipex.com/
Received on Fri Sep 13 2002 - 15:03:01 BST