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L811-EB Hardware User Manual Page 28 of 47
Since the module supports USB 2.0 High-Speed, it is required to use TVS diodes with equivalent
capacitance of 1pF or smaller ones on the USB_DN/DP differential signal lines, it is recommended to use
0.5pF TVS diodes. There is no special requirements for TVS diodes on VBUS pin, normally the 8 ~ 10pF
TVS diodes can be used.
USB_DN and USB_DP are high speed differential signal lines with the maximum transfer rate of 480
Mbit/s, so the following rules shall be followed carefully in the case of PCB layout:
USB_DN and USB_DP signal lines should have the differential impedance of 90 ohms.
USB_DN and USB_DP signal lines should be parallel and have the equal length, the right angle
routing should be avoided.
USB_DN and USB_DP signal lines should be routed on the layer that is next to the ground layer,
and wrapped with GND on both sides and layers.
3.5
USIM Interface
The L811-EB module has a built-in USIM card interface, which supports 1.8V and 3.0V SIM cards.
3.5.1
USIM Pins
The USIM pins are described as follows:
Pin Pin Name
I/O
Reset Value Pin Description
Type
D15 VSIM1
PO
USIM power supply
1.8V/3.0V
E15 SIM1_RST
O
L
USIM reset
1.8V/3.0V
F15 SIM1_CLK
O
L
USIM clock
1.8V/3.0V
G15 SIM1_DATA
IO
L
USIM data,
internal pull up(4.7KΩ)
1.8V/3.0V
H15 SIM1_CD
I
T
USIM card
detect, pull up(390KΩ)
Active-high, and high level means
SIM card is inserted, and low level
means SIM card is
detached.
1.8V
3.5.2
USIM Interface Circuit
3.5.2.1
N.C. SIM Card Slot
The reference circuit design for N.C. (Normally Closed) SIM card slot is shown in Figure 3-12: