User's Manual

Page 46
E Series Data Radio – User Manual
© Copyright 2005 Trio DataCom Pty. Ltd.
Modbus
This selection configures the PAD driver with options automatically
set to implement the MODBUS protocol, e.g. 5 mSec timer.
Custom
Other configurations of the PAD driver can be selected via the
Custom button which displays a dialogue box to permit selection of
several configuration options as follows:
SLIP / DIAGNOSTICS
Handshaking
If the standard PAD is selected (i.e. any settings apart from
SLIP/Diagnostics), then flow control can be either hardware
handshaking, XON/XOFF protocol or none.
The XON/XOFF flow control is not possible when using either the
SLIP/Diagnostics protocol.
The Handshaking section of the screen allows the selection
of either of the handshaking methods as well as allowing
handshaking to be disabled.
Details of the two handshaking methods are given below.
Hardware
The modem acts as Data Communications Equipment (DCE) and
supplies to the host controller the following interface signals:
Data Set Ready (DSR)
Data Carrier Detect (DCD)
Clear To Send (CTS)
Receive Data Output (RXD)
The host controller must act as Data Terminal Equipment (DTE)
and supplies to the modem the following interface signals :
Data Terminal Ready (DTR)
Request To Send (RTS)
Transmit Data Input (TXD)
• DCD
DCD has several modes of operation. It is set to TRUE when
data is being transferred from the modem to the host - RXD
line active. The signal is asserted approximately 500ms
before the start bit of the first character in the data stream and
remains for approximately 1 character after the last bit in the
data stream. The other modes of operation are dependent on
the advanced settings.
Part I – TVIEW+ Management Suite - Programmer
SLIP is a well known protocol for transferring binary data
packets over a data link. Each data packet is delineated by
<FEND> characters, and a substitution mechanism exists
that allows these characters to be included in the data
packet. Appendix B describes the SLIP protocol which is
used extensively in UNIX™ based systems, and is closely
associated with TCP/IP networks.
The diagnostics controller package uses the SLIP protocol to
communicate between base station and remote modems.
DNP-3 / IEC870
This selection configures the PAD driver to implement the
DNP-3 Protocol and IEC870 Protocol.
Pull Down Menu Selection
The PAD driver can be configured for a number of vendor
specific protocols by selecting the desired option.
Custom Format
This selection permits PAD driver to be configured in a variety
of ways and requires a greater understanding of the system
design.
For the modem to successfully transmit its packets (or
frames) of data over the radio channel, it must be told on
what basis to delineate data packets received at the data
port. Once the end of a data packet has been received at the
port the data frame is closed and transmission over the radio
channel commences. Delineation of data packets can be
configured to occur via any combination of:
• A pre-defined minimum time delay between packets
received at the port. Typically the time delay would reflect
the absence of a couple of characters in the data stream
at the specified user port baud rate.
• Limiting the maximum number of characters which can be
put in the data frame sent over the radio channel.
• Receipt of a selected end of message (EOM) character at
the port. An ASCII carriage return (character 13) is often
used for this purpose.
As each data frame to be transmitted over the radio channel
has overhead data consisting of checksums and SID codes.
The system designer must determine the best compromise
between the ratio of overhead versus user data which
depends on packet size and user data packet transmission
latency.
The fields which can be configured are:
• Character Input timer: Set the input timer value in ms or
enter zero to disable. Range 0 - 255.
• Maximum Frame Size: Set the maximum number of
characters or enter zero to disable. Range 0 - 4095.
• EOM Character: Select the check box to the left of the