User's Manual

Smart Machine Smart Decision
SIM868_Hardware_Design_V1.00 30 2016-06-20
If the voltage of UART is 5V, the following reference circuits are recommended:
VDD_EXT
4.7K
47K
UART1_TXD
4.7K
Module
VDD_EXT
RXD
VDD
DTE
Figure 21: TX level matching circuit
VDD
_
EXT
4.7K
47K
4.7K
DTE
UART1_RXD
Module
VDD_EXT
TXD
VDD
Figure 22: RX level matching circuit
4.5.3 Debug Interface
SIM868 could achieve software debug function through USB interface. When powering on the module, connect
USB_VBUS, USB_DP, USB_DM, 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
GND
GND
22R
USB_VBUS
VBUS
1uF
USB_DM
USB_DP
USB_DM
22R
USB_DP
Figure 23: USB reference circuit
The TVS on USB data line should be less than 5pF, and traced by differential forms.