Users Manual

GSM/GPRS Module Series
M66 Hardware Design
M66_Hardware_Design Confidential / Released 36 / 82
 RI: Ring indicator (when there is a call, SMS or URC output, the module will inform DTE with the RI
pin).
 DCD: Data carrier detection (the validity of this pin demonstrates the communication link is set up).
Hardware flow control is disabled by default. When hardware flow control is required, RTS and CTS
should be connected to the host. AT command AT+IFC=2,2 is used to enable hardware flow control. AT
command AT+IFC=0,0 is used to disable the hardware flow control. For more details, please refer to the
document [1].
The Debug Port:
 DBG_TXD: Send data to the COM port of computer.
 DBG_RXD: Receive data from the COM port of computer.
The Auxiliary UART Port:
 TXD_AUX: Send data to the RXD of DTE.
 RXD_AUX: Receive data from the TXD of DTE.
The logic levels are described in the following table.
Table 7: Logic Levels of the UART Interface
Table 8: Pin Definition of the UART Interfaces
Parameter Min. Max. Unit
V
IL
0 0.25×VDD_EXT V
V
IH
0.75×VDD_EXT VDD_EXT +0.2 V
V
OL
0 0.15×VDD_EXT V
V
OH
0.85×VDD_EXT VDD_EXT V
Interface Pin Name Pin No. Description
UART Port TXD 17 Transmit data
NOTE