[linux-dvb] Re: DVB-S 1.6: Grundig 29504-491 with TSA 5522 tuner chip.

[Johannes Stezenbach <js@convergence.de>]

Dr. Werner Fink wrote:
> 
>       some questions for the real experts.

Not me then, when it comes to frontends. Anyway...

> Accordingly to
> 
> http://www-us2.semiconductors.philips.com/acrobat/datasheets/TSA5522_2.pdf
> 
> the function tsa5522_set_tv_freq() in frontends/grundig_29504-491.c,
> does not use the Charge-Pump bit CP in the third byte:
> 
>         u8 buf [4] = { (div >> 8) & 0x7f, div & 0xff, 0x8e, 0x00 };
>                                                       ^^^^
> 
> with the CP bit high the value would be 0xce.  Is this intentional,
> that means this make no sence on the DVB-S 1.6 tuner layout?
> Or, which would be more a problem, would it be dangerous for the
> DVB-S 1.6 hardware to set this bit high?

AFAIK the charge pump setting has nothing to do with the tuner
layout. A high setting means that the voltage at the varactor
can change faster, but due to overshoot it may actually take
longer to reach a stable frequency. OTOH I think it is usually a good
idea to set the CP setting low *after* tuning for better stablity.

If the data sheet does not document the best CP setting one can
only experiment. You cannot damage your hardware by doing so.

> Also the last byte may have some values for the last three bits
> enabled because table 6 of the pdf at page 7 does not know all
> bits low.
> 
> Maybe a value 0x04 for 0.4Vcc1 (band B????) or something else
> has to be set.

I've no idea how the tsa5522 pins are connected in the
Grunding frontend. It is well possible that they are unused.

Johannes