User's Manual

MC55/56 Hardware Interface Description
Confidential / Preliminary
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MC55/56_hd_v03.00 Page 51 of 104 16.08.2005
3.9 Serial interfaces
MC55/56 offers two unbalanced, asynchronous serial interfaces conforming to ITU-T V.24
protocol DCE signalling. The electrical characteristics do not comply with ITU-T V.28. The
significant levels are 0V (for low data bit or ON condition) and 2.65V (for high data bit or OFF
condition). For electrical characteristics please refer to Table 26.
The GSM engine is designed for use as a DCE. Based on the conventions for DCE-DTE
connections it communicates with the customer application (DTE) using the following signals:
ASC0
• Port /TXD @ application sends data to the module’s /TXD0 signal line
• Port /RXD @ application receives data from the module’s /RXD0 signal line
ASC1
• Port /TXD @ application sends data to module’s /TXD1 signal line
• Port /RXD @ application receives data from the module’s /RXD1 signal line
GSM module
Application
/TXD
/RXD
/RTS
/CTS
/RING
/DCD
/DSR
/DTR
/TXD
/RXD
/RTS
/CTS
1
st
serial interface
(DTE)
(DCE)
2
nd
serial interface
ASC0 interface
ASC1 interface
/TXD0
/RXD0
/RTS0
/CTS0
/RING0
/DCD0
/DSR0
/DTR0
/TXD1
/RXD1
/RTS1
/CTS1
Figure 15: Serial interfaces