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DSB75 Development Support Board Rev. B1 Hardware Description

Strictly confidential / Released

DSB75_hd_v08 Page 32 of 94 29.09.2005

3.5.2 Serial Interface 2 (COM2)

The 2

serial interface COM2 (X202) of the DSB75 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 two control lines

RTS/CTS.

A level converter D201 adapts and inverts the V.24 signals (2.9V level) from the GSM

module to the RS-232C level.

The output lines are switched off (high impedance) if the GSM module is in POWER DOWN

mode. Therefore the PWR_IND signal is used to enable and shut down converters.

There are two alternative approaches to configure the ASC1 lines:

• as SD card interface (see section 3.10.2)

• as SPI interface (see section 3.10.3)

For using ASC1 lines at the test pins X101/X102 without a RS-232 level shifter, the switches

S300, S302, S304 and S306 have to be set to position 1.

Table 10: Pin assignment of 2

serial interface COM2 (X202)

X202

Name I/O Description X100

signal

name

Config.

switches

Remark

2 RXD O Receive Data RXD1 S302:3

S303:1

3 TXD I Transmit Data TXD1 S300:3

S301:1

5 GND - Ground GND

7 RTS I Request To Send RTS1 S304:3

S305:1

8 CTS O Clear To Send CTS1 S306:3

S307:1

1, 4,

6, 9

nc= not connected

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