3 switching the gt864 terminal on and off – Rainbow Electronics GT864-PY User Manual

Page 10

GT864-QUAD/PY Hardware User Guide

1vv0300756

Rev.0 08/ 05/07

page 10 of 23

3.3 Switching the GT864 Terminal ON and OFF

In this paragraph will be explained the way to switch the GT864 Terminals ON or OFF.

There are two ways to switch on the modem, once power is applied.

• either assert TO_IN high for > 0.2s;
• or activate the RS232 control line DTR, high for > 0.2s.

The modem is fully operational after 4 seconds. Logging onto a network may take longer than this and
is outside the control of the modem. The modem can be configured to start up at the time power is
applied by permanently tying power connector signals TO_IN (pin 4) and VCC (pin 1) together. In this
case DTR must be used to switch the modem on again after it has been switched off or reset, while
power is still applied.
NOTE: DTR must be cycled from low to high.
NOTE: The TO_IN signal requires a positive “edge” (a “sharp” signal transition from low to high) to
turn the modem on. This transition should be a rising signal from 0V (GND) to VCC, or at least a large
fraction of that voltage range, and must be applied at the same time as VCC or after it. Very slow
transitions (significantly slower than many milliseconds) or very small transitions (e.g. only a few volts
instead of 0V to VCC) will not turn on the module (since they are not considered to be a “positive
edge”).
Although this will not be an issue in almost all typical applications of the modem, under the following
condition special design care has to be taken:

•

large capacitors in your power supply which will lead to slow leading and falling edges (issue

does not apply with modern stabilized switching regulator power-adaptors) AND TO_IN tied in
parallel to VCC (instead of separate dedicated digital signal)

•

slow analogue signals used to assert TO_IN

•

TO_IN is asserted before VCC is asserted

All 3 cases above might prevent the modem from recognizing the power-up signal this is no failure of
the modem itself, the same would apply to almost any electronic device that provides a separate
“power-on” or “reset” signal.
If you are in doubt, please

•

use the mains power adapter that is provided by your distributor and is known to work

properly with your modem

•

make sure that your signal and system design is according to the above

•

consult our support team that will be more than happy to assist you.

There are three ways to switch off (power down) the modem as described below:

•

either use the AT#SHDN command;

•

HR_IN t=? (defined in the paragraph 3.1.1)

•

DTR permanently to GND

A delay of up to 10s is experienced as the modem logs off the network

A full system reset, independent of the status of the software, may be applied to the
modem as follows:

•

HR_IN t=? (defined in the paragraph 3.1.1)