User's Manual

5-1
Chapter 5
Before you begin programming…
The RF Terminal operates in two basic ways:
One-Way communication, where all data transfer is initiated by the RF
Terminal. The Base Station itself simply acknowledges the receipt of the data
by echoing it back to the Terminal. The host computer has no dialog
whatsoever with the Base Station or Terminal; it is simply used to take the data
coming from the Base through the serial port and do something with it.
Two-Way communication, where messages from the host user program are
sent to the Base Station (via the serial port), then from the Base Station to the
RF Terminal. The Terminal responds back to the Base with data and its
Terminal ID. The data is then transmitted from the Base to the host computer
where it is processed and the next command is sent out. Each RF Terminal has
a unique Terminal ID, allowing a single Base Station to handle up to 16
Terminals.
Two-way dialog is established when a Terminal SIGNS ON to the RF network.
The host computer application waits until a Terminal SIGNS ON, then begins its
processing by sending the first prompt out to the Terminal via the Base Station. If
the Terminal does not receive a prompt from the host, it goes into “sleep” mode,
“waking up” and checking with the Base periodically (see Chapter 3; Operational
Theory for details) to see if it has any messages waiting. This conserves battery
power and reduces radio traffic.
Two-Way mode requires programming to communicate with the Terminal
where One-Way mode does not. We have tried to make it easy for the
programmer to communicate with the Base Station; no protocol or handshaking
is required. This type of communication is fine when the Base is located only a
few feet from the serial port it is connected to. If you are locating your Base
Station farther away, use shielded, grounded (bare wire Pin 1 touching shield)
cable, lower baud rates and possibly, line drivers for very noisy environments.
Before you begin programming, there are some factors you should take into
consideration during the planning process.
• Plan for system failures. This includes hardware failures, software
failures and operator failures. In order to create an efficient application,
you must put some thought into what you will do when different parts of
the system fail.