About GSM modem

Andy Green andy at openmoko.com
Thu Feb 21 16:52:48 CET 2008

Hash: SHA1

Somebody in the thread at some point said:

> I remove the S3C2442 in GTA02A5, 

Wah that was quick!

> and GSM_MODEM’s TX and RX connect to
> Debug board’s RX and TX.
> When the GSM_MODEM enters the deep sleep mode and the current only is 4-5mA.

Well it is good if I understood it, it is what we can hope for.

> After GSM_MODEM enters sleep mode, I remove these UART net of GSM_MODEM
> from Debug board.
> I measuring these GSM_Modem’s pin connect to S3C2442.
> TX_MODEM : 2.9V

OK did we remove the pullup on TX_MODEM on this board?


One of these should float since it is an input?

> CTS= 0v
> RTS= 0v

One of these should float since it is an input?

When you measure with a scope probe, a good trick is to estimate the
source impedence of the signal by putting your finger on the scope probe
too on and off.  By seeing the amplitude of the mains "hum" you inject
you can guess the source impedence (==floatingness) is low or high.

> INT0: Floating
> INT0=2.9V

I didn't get why INT0 shows floating AND 2.9V here.

> I think maybe some wrong settings make our GSM_MODEM can’t enter sleep mode.

If I understood it, you are in a good sleep mode if we only pull 4-5mA
with GSM modem "on"?

> Do you have any idea?

What is the level for Vbat at this time?  2.9 sounds like a diode-ish
drop away from maybe 3.3V.  Is Vbat really still ~3.6V?

- -Andy
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