LTE Standard Module Series
EC21 Mini PCIe Hardware Design
EC21_Mini_PCIe_Hardware_Design 28 / 67
3.6. UART Interface
EC21 Mini PCIe provides one main UART interface. The main UART interface supports 9600bps,
19200bps, 38400bps, 57600bps, 115200bps and 230400bps baud rates, and the default is 115200bps.
This interface supports RTS and CTS hardware flow control, and be used for AT command
communication and data transmission.
The following table shows the pin definition of the main UART interface.
Table 9: Pin Definition of Main UART Interface
The signal level of main UART interface is 3.3V. When connecting to the peripheral MCU/RAM,
customers need to pay attention to the signal direction. The reference circuit is as follows:
MCU/ARM
TXD
RXD
UART_RXD
UART_TXD
UART_RTS
UART_CTS
RTS
CTS
GND
Module
GND
Voltage level: 3.3V
Voltage level: 3.3V
Figure 7: Reference Circuit of Power Supply
Pin Name
Pin No.
I/O
Power Domain
Description
UART_RX
11
DI
3.3V
UART receive data
UART_TX
13
DO
3.3V
UART transmit data
UART_CTS
23
DI
3.3V
UART clear to send
UART_RTS
25
DO
3.3V
UART request to send
