DSB75 Development Support Board Rev. B1 Hardware Description
Confidential / Released
DSB75_hd_v12
Page 33 of 96
2008-08-26
3.5.1
Serial Interface 1 (COM1)
The 1
st
serial interface COM1 (X201) of the DSB75 is intended for the communication
between the GSM module and the host application. This RS-232C interface is a data and
control interface for transmitting data, AT commands and providing multiplexed channels etc.
All modem status lines are available.
A level converter D200 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) while the GSM module is in POWER
DOWN mode. Therefore the PWR_IND signal is used to enable and shut down converters.
The rising edge of the DTR line voltage generates an ignition signal (impulse) via the V420
differential circuit so that it is possible to turn on the GSM module from the host, by plugging
in the serial cable or by remote control.
The USC lines (USC1, USC2) can be used as an alternative to the standard ASC0 lines
(RXD0, TXD0). In this case the switches S200, S201 have to be set to position 3. The
usability of the USC lines depends on the software configuration of the GSM module and is
for internal use only.
Table 11: Pin assignment of 1
st
serial interface COM1 (X201)
X201
pin
Name
I/O
Description
X100
signal
name
Config.
switches
Remark
1 DCD
O
Data Carrier Detected
DCD0
RXD0 S200:1
2 RXD
O
Receive
Data
USC1
S200:3
For internal use
only
TXD0 S201:1
3 TXD
I Transmit
Data
USC2
S201:3
For internal use
only
4
DTR
I
Data Terminal Ready
Note:
Low-to-high transition of
the DTR line activates the
ignition signal of the GSM
module.
DTR0
5 GND
- Ground
GND
6 DSR O Data
Set
Ready
Attention: Switch DSR0_I
(X122) must be set to DSR0_I
position.
DSR0
7
RTS
I
Request To Send
RTS0
8
CTS
O
Clear To Send
CTS0
9 RING
O
Ring
Indication
RING0
