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SIM800L(MT6261)_Hardware Design_V1.01 31 2016-07-07
VDD_EXT
4.7K
47K
4.7K
DTE
RXD
Module
VDD_EXT
TXD
VDD
Figure 24: RX level matching circuit
Note: When Figure22, Figure 23 and Figure 24 are used for electrical level isolation, if customers use serial port to upgrade SW,
please note VDD_EXT has no voltage output during the upgrading process, LDO output could be used as VDD_EXT in the
figure, upgrading through USB port is recommended.
4.5.3 Debug Interface
SIM800L could achieve software debug function through USB interface. When powering on the module, connect
VBUS, USB_DP, USB_DN, and GND to PC, then install the driver following the prompts, a UART port could
be recognized by PC, customer could achieve the software Debug with this UART port.
SIMCom recommended the following connected diagram:
Module
USB
USB_DP
USB _ DN
USB _ DN
GND
GND
22R
USB _ DP
USB_VBUS
VBUS
22 R
1uF
Figure 25: USB reference circuit
The TVS on USB data line should be less than 5pF, and traced by differential forms.
Note: please reserve the USB interface or test point for the further debugging
Table 11: VBUS operation voltage
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