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AC75 Hardware Interface Description
Strictly confidential / Preliminary
3.12
USB Interface
AC75 supports a USB 2.0 Full Speed (12Mbit/s) device interface. It can be operated on a
USB 2.0 Full Speed or High Speed root hub (a PC host), but not on a generic USB 2.0 High
Speed hub which translates High Speed (480 Mbit/s/) to Full Speed (12 Mbit/s).
The USB port has different functions depending on whether or not Java is running. Under
Java, the lines may be used for debugging purposes (see [8] for further detail). If Java is not
used, the USB interface is available as a command and data interface and for downloading
firmware.
The USB I/O-pins are capable of driving the signal at min 3.0V. They are 5V I/O compliant.
To properly connect the module's USB interface to the host a USB 2.0 compatible connector
is required. Furthermore, the USB modem driver delivered with AC75 must be installed as
described below.
The USB host is responsible for supplying, across the VUSB_IN line, power to the module's
USB interface, but not to other AC75 interfaces. This is because AC75 is designed as a self-
powered device compliant with the "Universal Serial Bus Specification Revision 2.0"
MCU
Transceiver
Baseband controller
2
The specification is ready for download on
AC75_HD_V00.202
3.2V
lin.
Regulator
PSU
USB
Figure 18: USB circuit
http://www.usb.org/developers/docs/
Page 56 of 120
VUSB_IN
5V
1.5kOhms
USB_DP
22Ohms
USB_DN
22Ohms
GSM module
s
2
.
VBUS
GND
D+
D-
Host
27.04.2006
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