SIMtrace prototype bug report

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Harald Welte laforge at gnumonks.org
Sun Jun 19 19:51:13 UTC 2011


Hi Sylvain,

On Sun, Jun 19, 2011 at 06:54:35PM +0200, Sylvain Munaut wrote:
> >> > However, I think there's one pretty serious problem in the hardware
> >> > design:  The bus switch has something like at least 5 (rather 16Ohms) of
> >> > internal 'on' resistance between the sim card and the phone.  While this
> >> > _might_ still work for I/O, nRST and CLK lines, it definitely doesn't
> >> > fly for the supply voltage (VCC).
> 
> Why not just keep the bus switch IC for the signals. ( ~ 20 ohms won't
> be a problem for sure ).

well, if you're sure the ~20 ohms is not a problem, then I think we can
indeed stop searching for a proper switch.  The big question is though:
Why does it not work yet?

The nRST, CLK and I/O are still routed via the switch.   The switch is
in the correct position, as I can apply 3.3V with a 10kOhm resistor to
any of the three lines on the 'phone' side, and I can see the
corresponding signal changing on the SIM card side.  However, the
high-voltage is only about 2.5V on the SIM card side.

Vcc is supplied permanently from the SAM7 to the SIM card socket. 

Still, no communication between phone (or smart card reader that I use
instead of a phone) and the SIM card is possible at this time.

Hopefully Kevin has some ideas tomorrow (he'll be visiting me to help
debugging).

Regards,
	Harald
-- 
- Harald Welte <laforge at gnumonks.org>           http://laforge.gnumonks.org/
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