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L816-AM Hardware User Manual
Page 27 of 42
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 requirement 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 be wrapped with GND on both sides and layers.
3.5
USIM Interface
The L816-AM module has a built-in USIM card interface, which supports 1.8V and 3V SIM cards.
3.5.1 USIM Pins
The USIM pins are described as follows:
Pin Pin Name
I/O
Reset Value Pin Description
Type
20
VSIM1
PO
USIM power supply
1.8V/3V
18
SIM1_RST
O
L
USIM reset
1.8V/3V
19
SIM1_CLK
O
L
USIM clock
1.8V/3V
17
SIM1_DATA
I/O
L
USIM data with internal 4.7KΩ pull-up
1.8V/3V
26
SIM1_CD
I
USIM card detection with 390KΩ pull up.
Active-high, and high level means SIM
card is inserted; and low level means SIM
card is detached.
1.8V
