Tony Duell wrote:
[snip]
> What it _won't_ do is decode PAL (or any other) colour video. There's
> a separate chip for that in the TV.
I don't WANT it to decode PAL. I'm using it for a display system in a
selfbuilt computer. I'm going to add a video tuner later (i.e. when I've
reverse-engineered one of the VCR tuners in my junk^M^M^M^M quality used
parts box).
> The RGB outputs from the teletext
> board are combined with that chip. There's often another output from
> the teletext board which is used to blank the 'live' video. So you
> can have live video only (teletext decoder produces no RGB ouptuts),
> teletext only (teletext decoder produces RGB _and_ blanks live video)
That's the mode I'm planning to use it in.
>> 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
> I doubt the PICDREAM will produce a valid teletext data stream...
I don't want it to generate a TTX data stream. I want it to generate a video
signal for the TTX to lock onto and the Cub to sync to. I don't care if it
has no TTX data to lock onto - I can just load its RAM and send it a
"DISPLAY ON" command.
>> 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
> Have you tried the local public library? Main ones often have the
> Radio and Television Servicing books, and the TX91 is likely to be in
> one of those. Alas my only collection of such books only goes up to
> 1981.
Might be worth a shot. Thanks. Now, I wonder if the central library is open
on a Saturday...
> Be warned that when they changed the teletext decoder board they may
> also have changed the control microcontroller. So it's not definite
> that your board repsonds to the same commands as the SAA52xx series.
I think I've got the MCU somewhere. Don't know if it still works, though.
>> Know anyone that stocks the SAA5243? Can't find it on Farnell's
>> site, nor does my CPC catalogue list it.
> Grandata used to do it (I bought one from there to use in a very
> simple I2C colour video display (4 chips IIRC -- the SAA5243, a
> 74LS04 (clock oscillator, mostly), a 6264 RAM and a 74LS244 (output
> buffer)).
Ooh - another company to track down :-)
> See if you can track down the Teletext PCB from a Thomson ICC5
> chassis. It would be ideal for you. There are several versions, but
> every one I've seen contains an SAA5243, SAA5231 and a 6264 RAM. Some
> have a custom on-screen-display chip that you can easily desolder (to
> keep it off the bus). The support components are there too. From what
> I remmeber you need to feed it +12V (and/or +5V, I forget just what
> PSU components are on-board) and composite video. It's got a standard
> I2C bus to control it. The RGB outputs are transistor-buffered to
> strange levels, but you can either add a few more transistors to make
> them sane again or tap the signals off the SAA5243 pins.
Time to track down a junked ICC5 chassis. Anyone on here got one they don't
mind pulling the Teletext board out of? :-)
>> 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
> That only sets the on-screen display and/or the lamps on the range
> switch. It doesn't actually affect the operation of the 'scope (the
> probe is a passive /10 divider, the 'scope will always display the
> signal it receives). You can use any probe with the 466 (provided you
> can match it to the input capacitance of the 'scope), the extra
> contact is just to make it easier to read the range switch, etc.
Ah, right. So it doesn't matter if I use, say, a Velleman "professional" 10x
probe and leave the outer contact unconnected? Or I could just shove a piece
of tinfoil in there to short it out...
> IIRC, that pin is shorted to ground for the 'identify' mode (moves the
> trace vertically slightly and changes the on-screen-display to
> 'INDENTIFY' so you can tell which trace corresponds to the probe).
> It's connected to ground via a rrsistor to tell the 'scope what
> division ratio the probe is. Older 'scopes just support *1
> (open-circuit) and *10. Later ones support *100 (and maybe others)
> too.
The 466 seems to support 1x/10x only. No OSD either.
The trace does look a bit "grainy", but I guess that's because it's a
storage scope.
BTW, anyone interested in a Gould OS1100A? 30MHz, delay sweep, single
timebase, dual channel, no manual, a bit heavy. Make me an offer - buyer
collects or sends a courier round for it.
Later.
--
Phil.
philpem_at_dsl.pipex.com
http://www.philpem.dsl.pipex.com/
Received on Sat Sep 14 2002 - 02:28:00 BST