Specifications

XT55 Hardware Interface Description
Confidential / Preliminary
s
mo b i l e
XT55_hd_v00.02 Page 65 of 116 17.03.2004
3.12.2.2 Using the GSM_SYNC pin to control a status LED
As an alternative to generating the synchronization signal, the GSM_SYNC pin can be used
to control a status LED on your application platform.
To avail of this feature you need to set the GSM_SYNC pin to mode 1 by using the
AT^SSYNC command. For details see [1].
When controlled from the GSM_SYNC pin the LED can display the functions listed in Table
18.
Table 18: Coding of the status LED
LED mode Operating status
Off XT55 is off or run in SLEEP, Alarm or Charge-only mode
600 ms On / 600ms Off No SIM card inserted or no PIN entered, or network search in
progress, or ongoing user authentication, or network login in
progress.
75 ms On / 3 s Off Logged to network (monitoring control channels and user
interactions). No call in progress.
75 ms on / 75 ms Off / 75 ms On /
3 s Off
One or more GPRS contexts activated.
Flashing Indicates GPRS data transfer: When a GPRS transfer is in
progress, the LED goes on within 1 second after data packets
were exchanged. Flash duration is approximately 0.5 s.
On Depending on type of call:
Voice call: Connected to remote party.
Data call: Connected to remote party or exchange of
parameters while setting up or disconnecting a call.
LED Off = GSM_SYNC pin low. LED On = GSM_SYNC pin high (if LED is connected as illustrated in
Figure 24)
To operate the LED a buffer, e.g. a transistor or gate,
must be included in your application. A sample
configuration can be gathered from Figure 24. Power
consumption in the LED mode is the same as for the
synchronization signal mode. For details see Table
27, GSM_SYNC pin.
Figure 24: LED Circuit (Example)