Embedded Modem Developer's Guide

Chapter 6 – Fax Class 1 and Class 1.0 Commands
Multi-Tech Systems, Inc. SocketModem MT5600SMI Developer’s Guide 86
Chapter 6 – Fax Class 1 and Class 1.0
Commands
Fax I/O Processing
The fax I/O interface supports asynchronous serial and parallel interfaces. The character format is 8 bit
data, no parity, and 1 stop bit. Start and stop elements are removed from the transmit data and added to
the receive data. Both transmit and receive data are buffered. Flow control using XON/XOFF or RTS/CTS
is provided.
Unique control character strings are identified, filtered, or reinserted into the I/O data stream. These
control characters and their resultant action are described below.
DTE-to-Modem Transmit Data Stream
Characters Detected Action Taken
<DLE><data> Delete <DLE><data> characters.
<DLE><ETX> Recognize as a string terminator and take appropriate action.
<DLE><DLE> Replace with single <DLE> character.
Modem-to-DTE Receive Data Stream
Characters Detected Action Taken
<DLE> Insert extra <DLE> ahead of <DLE>.
The modem also identifies the end of a frame by inserting <DLE><ETX> into the data stream after the
FCS bytes.