[linux-dvb] Re: [RFC] USB DVB design

[Holger Waechtler <holger@convergence.de>]

Jean-Claude Repetto wrote:
> 
> Sorry, I have never used Eagle, so it will be done more easily by the author
> of the current schematic.

give it a try, it's pretty simple and nice. You get the free version on 
the homepage of http://www.cadsoft.de/.

I hope we won't need more than about 100x50mm PCB area so that we can 
even make the layout with the free version...


> First, we have to choose an IR receiver. The LIRC project recommends the
> Vishay TSOP1738
> (http://www.vishay.com/docs/tsop17.pdf), very easy to use. Only two
> resistors and a capacitor are needed (look at the application circuit on
> page 2 of the data sheet).
> 
> Then we have to choose on which pin of the FX2 it will be connected. I
> suggest the PA1/INT1 pin.

Do you want to make the IR code interrupt-driven? If so you have to 
consider that the INT1# is active low and it can trigger only to 
negative edges or levels. You would need some more external logic.

If you want to write the IR code polled I would suggest to use another 
pin to keep the interrupt input free.


> I have another question about the tuner interface :
> Since the FX2 is connected to a 3.3V power supply, Voh is guaranted to be
> only higher than 2.4V.
>
> Are the data bus and control bus of the tuner working in 5V or 3.3 V ? I'd
> like to look at the data sheet of the tuner to check if Vih(min) <= 2.4 V,
> but I have not found it (I suppose you have it, but perhaps there is a NDA
> ?).

The FX2 inputs can accept 5V logic levels (for the parallel MPEG TS 
interface). On reset and wakeup pins 3.3V logic is used.

The i2c interface is pulled up by the 2k2 resistors to 5V level for the 
EEPROM. i2c interfaces pull down the signal to ground if they are 
talking to the bus - so it's pretty easy to interface 3.3V and 5V logic.

Holger



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