Worth Data RF Terminal 7000 - Manual (Page 39)

cable distance allowable.
The gating factor for the application is almost always going to be the application program. By splitting the
application between two or more work stations, each talking to a separate set of Terminals/Base Station,
that factor can be minimized.
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. This is not very useful,
because it has no editing or prompting. 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 64 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. (Do not use Cat 5 wire for a serial cable).
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.
• Look for All Errors. Be sure your program is trapping all possible error conditions that the Base Station may
return to you. The list includes:
Sequence Errors detected
Illegal Command detected
Base Station Initialized
Addressing a Terminal Not Signed In
Command without an ID
All of these error conditions are detailed in the next chapter. Don’t forget to program for them;