SimCom SIM5218E Hardware Design page 28

SIM5218E Hardware Design
(Data Communication Equipment), following the traditional DCE-DTE (Data Terminal
Equipment) connection, the module and the client (DTE) are connected through the following
signal (as following figure shows).
Serial port
Port/TXD @ Client sends data to the RXD signal line of module
Port/RXD @ Client receives data from the TXD signal line of module
All pins of all serial ports have 8mA driver, the logic levels are described in following table
Table 8: Logic levels of serial ports pins
Parameter
Logic low input
Logic high input
Logic low output
Logic high output
Note: VDD_EXT=2.6V, is module internal IO reference voltage.
SIM5218E provides an AT command to support Null modem. Null modem mode uses two lines
(RXD, TXD(GND not comprised)) to setup communication between devices. The lines
connection is as below.
SIM5218E_HD_V1.03
Figure 12: Interface of serial ports
Min
0
0.7 *VDD_EXT
GND
VDD_EXT -0.2
27
Max Unit
0.3*VDD_EXT V
VDD_EXT +0.3 V
0.2 V
VDD_EXT V
11.06.2009