Usb Interface - Fibocom L850-GL Series Hardware Manual

should be at least 3 times the line width (≥ 3W). The largest spacing between the bended part of the
serpentine line and another one of the differential lines must be less than 2 times the spacing of normal
differential lines (S1 < 2S);
PCIe Difference Pair 1
PCIe Difference Pair 2
The difference in length of two data lines in difference pair should be within 5mil, and the length

match is required for all parts. When the length match is conducted for the differential lines, the
designed position of correct match should be close to that of incorrect match, as shown in Figure 3-
15. However, there is no specific requirements for the length match of transmit pair and receiving
pair, which means the length match is only required by intra differential pair rather than inter
differential pair.
Dismatched end

3.4.2 USB Interface

The L850 module supports USB2.0 which is compatible with USB High-Speed (480 Mbps) and USB Full-
Speed (12 Mbps). It supports USB3.1 Gen1 using for LTE cat9 high speed data throughput at the same
time. For the USB timing and electrical specification of L850 module, please refer to "Universal Serial Bus
Specification 2.0" and "Universal Serial Bus Specification 3.0".
USB interface initialized with host driver, and then mapped NCM and ACM ports in Chrome/Linux/Android
OS. The NCM ports are used for data transfer. The ACM port is used for AT command. The port can be
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FIBOCOM L850-GL Series Hardware Guide
≥3W
W
S S1<2S
≥20mil
Figure 3-14 Requirement of PCIe line
Correct match
Figure 3-15 Length match design of PCIe difference pair
≥1.5W
Matched end
Incorrect match
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