Sierra Wireless AIRPRIME WISMO218 - Manual (Page 41)

WA_DEV_W218_PTS_002 Rev 006 April 29, 2010 41
Product Technical Specification &
Customer Design Guidelines Interfaces
Customer application
( DTE )
WISMO218
( DCE )
ON/~OFF
CT103/TXD
CT104/RXD
~CT105/RTS
~CT106/CTS
37
39
40
38
GND
Rx
RTS
CTS
GND
Tx
41
42 ~CT107/DSR
44
~CT108/DTR
~CT109/DCD
~CT125/RI 45
43 DCD
RI
DSR
DTR
Figure 10. Example of V24/CMOS Serial Link Implementation for 5-wire UART
The designs shown in Figure 8, Figure 9, and Figure 10 are basic designs. Both the DCD and RI can
be left open when not used.
However, a more flexible design to access this serial link with all modem signals is shown below.
Customer application
( DTE )
WISMO218
( DCE )
GND
ON/~OFF
~CT107/DSR
~CT109/DCD
~CT108/DTR
~CT125/RI
37
43
44
45
42
GND
DCD
DTR
RI
GND
DSR
CT103/TXD
CT104/RXD
~CT105/RTS
~CT106/CTS
41
39
40
38
Rx
RTS
CTS
Tx
2x 10K
2.8Volt
Figure 11. Example of Full Modem V24/CMOS Serial Link Implementation for full-UART
There is an internal 10K  pull-up resistor on RI and DCD to set it to HIGH level during the reset state.
The UART interface is a 2.8V type, but is 3V tolerant.
Tip: The AirPrime WISMO218 UART is designed to operate using all the serial interface signals. In
particular, it is recommended to use ~CT105/RTS and ~CT106/CTS for hardware flow control in order
to avoid data corruption during transmission.