JF2 Hardware User Guide
1vv0300985 Rev.4 2013-04-09
Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights Reserved.
Page 11 of 40
Mod. 0805 2011-07 Rev.2
If the product containing the JF2 needs to support abrupt removal of power, then the module
will require a cold start reset upon reapplication of power.
2.3.
Understanding ON-OFF and SYSTEM-ON
ON-OFF: Input control
SYSTEM-ON: Output indicator
The JF2 power is controlled by a state machine. This state machine is clocked by the internal
32 KHz RTC clock, and is controlled by internal signals as well as the ON-OFF and NRESET
signals. The SYSTEM-ON signal reflects the power state of the JF2: logic low for hibernate
mode, and logic high for full power mode.
When power is first applied to the JF2, the internal RTC must start up before the state
machine can begin operating. ON-OFF signals applied before the state machine is ready for
them will be ignored. The JF2 signals the readiness to accept ON-OFF signals by outputting a
pulse on the SYSTEM-ON line after power is first applied. This pulse is only output upon
application of power, and is not output when the receiver is in hibernate or full power mode.
The ON-OFF signal is normally low. When it transitions high, it should stay high for a time
equivalent to a minimum of 3 RTC clock cycles. The signal may then transition low and
remain low until the next change in power state is desired.
A single OR gate with one input being SYSTEM-ON and the other being an external pulse
will allow the module to be turned back on with a suitable pulse, but it will not be possible to
use a second pulse as it is blocked with the SYSTEM-ON signal. The only option to place the
module in hibernate state is to issue the serial command.
If full ON-OFF control is desired along with having SYSTEM-ON auto-start the receiver,
then additional logic is needed to detect the first falling edge of SYSTEM-ON and using this
detection to gate off the SYSTEM-ON signal to the ON-OFF signal.
If GPIO8 is pulled to logic 1, then the ON-OFF input is modified to be just an ON input. It
would not be possible to place the JF2 into hibernate by pulsing ON-OFF in this case.
2.3.1.
Auto-ON Configuration (GPIO8 Control)
The JF2 powers up directly into the hibernate state. It is possible to have the module
automatically transition to the full power state by tying the SYSTEM-ON output to the ON-
OFF input. GPIO8 should also be tied high, which changes the ON-OFF signal to just an ON
signal. However, this implementation eliminates the possibility of using the ON-OFF signal
to change power states and eliminates the SiRFAware™ and Push-to-Fix™ power modes. If
the serial command to place the JF2 in hibernate mode is issued, the module will transition to
the hibernate state with no way other than removal and reapplication of power (with resulting
RTC and SRAM data loss) to force the module to power up. For some users, this may be all
that is required if time and data retention are not important during a power down situation.