DSB75 Development Support Board Rev. B1 Hardware Description
Confidential / Released
DSB75_hd_v12
Page 43 of 96
2008-08-26
3.8
USB Device Interface
DSB75 supports a USB 1.1 Full Speed (12 Mbit/s) device interface. It is primarily intended
for use as command and data interface and for downloading firmware.
The second USB interface with mini AB connector (X111) is reserved for future use and has
been not described.
Figure 21 shows the simplified interface schematic. Figure 22 shows the placement of the
USB connectors, switches, jumper and the pin location. Electrical characteristics are
specified in section 8.
DSB75 provides a USB B receptacle to connect a host device. The USB lines VBUS, D+, D-
are connected directly to the GSM module via slide switches S110 - S112 (position 3).
In series to VBUS line there is a jumper (X120) connected. It is set during normal operation
and may be used for remote control facilities.
The rising edge of VBUS voltage generates an ignition signal (impulse) via the differential
circuit V420. This way it is possible to turn on GSM module from the host, by plugging in the
serial cable or by remote control.
The EMC circuit protects the DSB75 and the GSM module against overvoltage (e.g. ESD).
The USB I/O pins are capable of driving the signal at minimum 3.0V. They are protected
from 5V input voltage driven from the host according to the USB specifications.
B2B
X100
USB_DP
USB_DN
VUSB_IN
D+
D-
VBUS
GND
1
3
1
3
1
3
S110
S111
S112
USB-B
X110
1
3
2
4
12
68
69
EMC
X120
Jumper
IGT
V420
56
d/dt
Figure 21: USB device interface
