User Manual

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USERS MANUAL
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2.7 Serial Data Interface
The serial channels are used as asynchronous communication links between the
application system and the module. The following table shows the serial data channels
related signals:
Pin Signal Description Dir
23
DCD
Data Carrier Detect
This signal is set default high. It goes low indicating that a data call
is established (CONNECT received from the remote modem). The
signal goes high when the data connection is disconnected.
O
25
CTS
Clear To Send
This signal is initially set high, indicating that the module is not ready
to receive data. It is set low after the module is done performing its
startup procedure indicating that it is ready to receive data.
O
26
DTR
Data Terminal Ready
This signal should be set low by the application during a data call. A
low to high transition will terminate the data call.
I
27
TD
Transmit Serial Data To Module (DTMS)
The application shall set this signal high at startup.
I
28
RTS
Request To Send
The application shall set this pin low when it is ready to receive data.
I
30
RD
Receive Serial Data From Module (DFMS)
The module will set this signal high at startup.
O
Table 15: Serial Data Channels
The common CMOS electrical specifications defined in Section 2.3.3 are valid for all
these signals. The standard character format is 1 start bit, 8 data bits, non-parity and 1
stop bit. In all, there are 10 bits per character.
Note! The signal levels do not match the standard RS-232 (V.28). If the application
signal levels are not compatible with the CMOS levels described in Table 3: CMOS
Output / Input Electrical Characteristics, then electrical protection level limiters or
level conversion hardware will be necessary between the CM-52 module and the
application.