DSB45 Development Support Box
Confidential / Released
s
DSB45_HD_V05
Page 20 of 50
01.02.2008
2.7.4
Application interface 2 (COM2)
The 2
nd
application interface COM2 (X202) of the DSB45 is intended for the communication
between the GSM module and the host application. This RS-232C interface includes only the
data lines RXD/TXD for transmitting GPRS data and AT commands and the control
RTS/CTS. The interface is accessible if the slide switches X104 – X107 are set to position
“Internal”.
COM2 can only be used if the GSM module includes a second serial interface (in [1] and [2]
referred to as ASC1).
A level converter adapts and inverts the signals from the GSM module from 2.65V to RS-
232C level.
The output lines are switched off (high-impedance), if the GSM module is in POWER DOWN
mode. After activating the module via IGT signal (ignition), the serial output lines are
undefined for approx. 300 ms. See [1] for details.
Table 7: Pin assignment of 2
nd
application interface COM2 (X202)
Pin no.
Designation
I/O
Function
1
-
-
Do not use this pin
2
RXD1
O
Receive Data 1
3
TXD1
I
Transmit Data 1
4 n.c.
5 GND
-
Ground
6
-
-
Do not use this pin
7
RTS1
I
Request To Send 1
8
CTS1
O
Clear To Send 1
9
-
-
Do not use this pin
As the X202 interface has only four lines, you may need a customized adapter cable for the
RS-232 connection. This is useful, for example, if your application also requires the lines
DSR, DCD, RING. In such a case it is recommended to use the following pin assignment:
1
5
9
6
9 pole Sub-D
on PC side
(female)
1
5
9
6
9 pole Sub-D
on DSB45 side
(male)
1
2 RXD
3 TXD
4
5 GND
6
7 RTS
8 CTS
9
1
2
3
4
5
6
7
8
9
DCD
RXD
TXD
DTR
GND
DSR
RTS
CTS
RING
Figure 7: Recommended adapter cable from PC to COM2 on DSB45
