User's Manual

Page 45
E Series Data Radio – User Manual
© Copyright 2005 Trio DataCom Pty. Ltd.
Part I – TVIEW+ Management Suite - Programmer
Settings
This menu permits selection of the PC serial port (COM1 to COM4)
to be used for communications with the unit. COM1 is the default
selection and if a different port is to be used it must be set before
establishing a session by reading the configuration from a unit.
Whilst a session is established with a unit this menu can not be
accessed.
Help
This menu permits selection of help information using the Contents
key. Warnings regarding use of the programmer software using the
Warnings key and version detail using the About key.Port A and
Port B Configuration
Data from these two user ports is multiplexed for transmission over
the air. Each port can be configured separately for the Character
layer (Data speed, number of data bits, number of stop bits,
parity), Packet layer and Handshaking (flow control). Port B must
be enabled if required by setting the check box at the top of its
configuration section.
If Port B is off, the 16K memory is split equally between Port A
Rx/Tx buffers (i.e. 8K & 8 K). If Port B is on, then the 16K is split
equally across Port A & B Rx/Tx buffers (i.e. 4K, 4K, 4K & 4K).
The following description is common to both ports.
Character Layer
There are two standard formats and a custom format that can be
selected by checking the appropriate control button to the left of
the description. The standard formats are:
• 9600,N,8,1 (data speed = 9600 bps, no parity, 8 data bits, 1
stop bit)
• 4800,N,8,1 (data speed = 4800 bps, no parity, 8 data bits, 1
stop bit)
A non-standard format can be selected via the Custom button that
displays a dialogue box to permit selection of data speed, parity,
number of data bits and stop bits. Once selected the OK button
should be used to complete the selection. The custom selection is
also displayed in the main window below the Custom button.
Packet Layer
There are two standard configurations and a custom configuration
which can be selected by checking the appropriate control button
to the left of the description. There are essentially two basic modes
of operation for the packet assembler and disassembler (PAD).
The first is where the PAD operates in a standard mode with data
received at the port being immediately sent over the radio channel.
The second is a store and forward or delayed mode where whole
data packets are received from the port before being sent over the
radio channel.
In both cases data is sent over the radio channel in variable
length frames and delineation of these frames is dependent
on the configuration selected as well as the characteristics
of the data stream received at the data port.
The packet layer configuration options which can be
selected are:
Standard (live framing)
With standard live framing data received from the host by the
modem is immediately placed into a frame and transferred onto the
radio channel.
This avoids placing “store and forward” delays in the data
transmission.
If a stream of characters is received by the modem, then several
characters at a time may be placed into the same frame. The
number of characters in the frame depends mainly on the
respective baud rates of the user port and the primary channel
baud rate of the modem, as well as the level of overheads
experienced on the radio channel and the user data stream.
For example a constant stream of 300 baud user data placed onto
a 9600 baud channel will result in 1 character per frame being
transmitted. If the user baud rate was lifted to 9600,N,8,1 with
a continuous data stream, then the frame size would settle to
about 16 characters plus 32 overhead bits. If collision avoidance
is enabled as master the average frame size will increase to 32
characters plus overhead bits.
The number of data bits associated with the user data stream will
also have an effect on the average size of a frame. For instance
the number of stop bits, and number of data bits per character.
The system designer must choose the best compromise of all
the above items to ensure the most efficient method of data
transmission.
Note: The first character is always packetised and sent by itself
regardless of all the above variables.