CEM600 EVDO Mini PCIE Module Hardware User Guide
Shang Hai YUGE Information Technology co., LTD
Page 12 of 25
Chapter 5. Main function interface description
5.1 UART interface (optional function)
Table 5-1 UART Interface Definition
Pin Signal name
I/O properties
High value
Description
11
UART1_RXD
Input
2.6V
UART1 data reception
13
UART1_TXD
Output
2.6V
UART1 data transmission
17
UART1_RI_N
Output
2.6V
UART1 ringing indication
23
UART1_CTS_N Input
2.6V
UART1 is ready to send
25
UART1_RFR_N Output
2.6V
UART1 request to send
31
UART1_DTR_
N
Input
2.6V
UART1 DTE is ready
33
UART1_DCD_
N
Output
2.6V
UART1 carrier detection
GND
Ground
The UART interface supports 3-wire or 8-wire serial protocols.
The UART interface supports the following features:
Software download upgrade
Data communication
AT Command
Bluetooth
When the UART interface is directly connected to the microprocessor, the reference
design is as follows. If the 3-wire connection is used, the RFR and CTS should be shorted.
Note that if the levels on both sides do not match, you can connect a 1k resistor in series with
the signal line or add a bidirectional Schottky diode.
Figure 5-1 UART interface and microprocessor connection reference design
The UART interface can also be connected to the standard RS232-C interface via an
RS232 level shifting chip. The MAX3232 chip is recommended. The reference design is as
follows:
