DSB75 Development Support Board Rev. B1 Hardware Description
Confidential / Released
DSB75_hd_v12
Page 35 of 96
2008-08-26
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 DSB75 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 13: Recommended adapter cable from PC to COM2 on DSB75
3.5.3
Debug Interface (COM3)
The debug interface COM3 (X205) of the DSB75 is reserved for internal software
debugging. It is a two wire interface with data lines only.
A level converter D201 adapts and inverts the V.24 signals (2.9V level) from the GSM
module to RS-232C level.
The output lines are switched off (high impedance) if the GSM module is in POWER DOWN
mode.
The ASC2 lines of the GSM module are used by default as GPIOs (see section 3.3)
Table 13: Pin assignment of debug interface COM3 (X205)
Pin
Name
I/O
Description
X100 signal
name
Config.
switches
Remark
2 RXD
O
Receive
Data
RXD2_GPIO9
S458:1
3 TXD
I
Transmit
Data
TXD2_GPIO10
S459:1
5 GND
-
Ground
GND
1, 4, 6,
7, 8, 9
nc
nc= not connected
