
APPENDIX
Protocol Data Mode
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5.1.2 Usage of RS-232 Interface
5.1.2.1 Connection of the interface
In protocol data mode only the interface signals TXDI and RXDO are used.
The modem lead signals DTRI, DSRO, DCDIO, and RIIO are not used. However the status
of the lead signals can be signalled over the protocol data channel.
5.1.2.2 Interface
parameters
The baud rate of the RS-232 interface is selected using the SPBD configuration command.
The actual baud rate can be retrieved with the GPBD command. A list of available baud
rates is shown in response to the IPBD command.
The baud rate setting is a local matter, i.e. the two peers of a connection may use different
baud rates at their ends.
In protocol data mode a baud rate of 115.200 Bd is generally recommended.
5.1.3 HDLC Frame Structure
A byte oriented (asynchronous) HDLC framing is implemented.
HDLC frame
FLAG
ADDR
CTRL
DATA
FCS
FLAG
A HDLC frame consists in a flag field (start byte), a variable length address, a control field,
payload data and a 16-bit frame check sequence.
5.1.3.1 Flag field (FLAG)
The frame is started by a 1-byte wide flag field. The flag field has the value 0x7E. All other
bytes of a frame must be different from that value. This is achieved through a transparency
algorithm (see section 5.1.4.2)
The frame is terminated by another flag field. In a continuous sequence of frames only one
flag byte is required as delimiter between frames. The flag field is also used as inter-frame
padding. So there may be multiple flag fields between two frames.