DSB75 Development Support Board Rev. B1 Hardware Description
Confidential / Released
DSB75_hd_v12
Page 79 of 96
2008-08-26
7
Turn on / off the GSM Module
All the hardware driven solutions described in [1] for turning on and off the GSM module are
implemented on the DSB75 and can be used by as follows:
7.1
Turn on the GSM Module
There are several ways to turn on the GSM module:
Non-locking ignition key S421:
The major approach is to switch on the connected GSM module by pressing the ignition
(IGT) switch S421 for at least 400ms. The ignition switch is located on the component side
of the DSB75.
A 2-pin jumper (X420) connected in parallel to switch S421 makes it possible to control the
IGT signal from a remote unit.
Toggling low-to-high state of DTR:
As an alternative to the ignition key S421, the GSM module can be activated by toggling the
DTR line available on COM1.
The high signal of DTR generates a low pulse on IGT which switches the module on. For this
purpose, the DSB75 uses a differentiator circuit comprising the RC combination C420, R420,
R421 and the transistor V420.
Note: Before activating DTR keep the lines inactive for at least 500 milliseconds (see chapter
8).
Plugging the USB cable:
Plugging in the USB cable to one of the two USB connectors triggers the IGT signal in the
same manner as DTR0. In this case, the USB supply voltage delivered from the USB host
starts the GSM module.
The 2-pin jumper (X120) connected in series with the USB voltage lines makes this function
remote controllable.
US
B
co
nn
ec
to
r
1
B
oa
rdt
oB
o
a
rd
co
nn
e
ct
o
r
VBUS_AB
DS
UB
9
R
S
232
(A
S
C
0
)
DTR
IGT
Jumper
Jumper
Ignition
switch
1M
220K
2u2
X420
S421
X203
X110
X201
X100
d/dt
PWR_IND
100k
220K
2u2
d/dt
100k
Jumper
X120
PWR_IND enables the LED-drivers,
RS232 drivers, pull-up resistors
Figure 48: Turn on circuit
