Wavecom GR64 Application Note - page 10
2.2.3 SIMDAT
The SIMDAT-line has a built-in 10k pull-up resistor implemented inside the Wireless
CPU. This pull-up resistance might not be enough to pass the IO type approval test
cases (27.17.2.5) depending on the application implementation. The application
should provide the capability of adding a pull-up resistor (R
IO
) from SIMDAT to
SIMVCC as close to the SIM-holder C7-pin as possible. The resistor can be in the
range from 6.8k and up. The resistance needed depends on the added capacitance
from the system connector SIMDAT-pin to the C7-pin of the SIM-holder. The C
VCC
capacitor added on SIMVCC will help alleviate this problem also.
The maximum current in the SIMDAT-line is limited to 1mA peak. If
the current exceeds that, even for a very short time (ns range) the
type approval test will fail. If this happens the R
IO
value should be
increased.
CAUTION
Provide the capability of adding capacitance on SIMVCC as close to
the SIM-holder as possible. The pad layout should support capacitors
up to 10uF.
Also provide the capability of adding an extra pull-up resistor ≥6.8k
in case the application adds capacitance. This will improve the rise-
time.
TIP
GR/GS64 Application Note
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SIM Interface
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