GPRS shield RTC

Products & Technology Shields
#1

i have now GPRS shield v1.0 ( ?0.9b) and v1.2

on arduino uno, using arduino 1.0.1
and would like to use the RTC from the SIM 900 chip

on v1.2 is a battery holder ( for CR1220 3V )

in the
SIM900_Hardware_Design_V2.00.pdf
say there MUST be a large capacitor, or a battery with diode or a rechargeable battery like XH414H-IV01E (Seiko)

in the v1.4 drawing i see a C6 connected parallel to battery holder / no diode/.
http://www.seeedstudio.com/wiki/images/0/0c/GPRSshield_Schematic.pdf

my board v1.2 i dont know.

testing AT commands get ERROR

must a battery be installed to get the RTC answer??

or does it only work together with time info from network??

[code]AT+CCLK

ERROR
AT+CLTS=?

+CLTS: “yy/MM/dd,hh:mm:ss+/-zz”

OK
AT+CLTS

ERROR[/code]

#2

ok, this worked, without a battery installed,

[code]AT+CCLK?

+CCLK: “12/08/02,15:21:28+28”

OK[/code]

must come from network

a other good test:

[code]AT+CUSD=1,“1019#”,15

OK

+CUSD: 0,"Your current balance is 71.85 Baht (valid until 13-Se2d0[/code]
with a small problem from the too small buffer of arduino softserial.