3-2
A little more in depth…
This RF system’s dialogue is Terminal initiated. The Terminal says, “I’m
here, give me something to do. The Worth Data RF system is different from
other systems in that our RF Terminal does not constantly “listen” for a data
prompt from the host. We decided to use a different approach that would
help to eliminate unnecessary radio traffic, conserve battery power, reduce
the size of the Terminal, and greatly simplify the base station's
logic/circuitry.
Here is how it works:
Each RF Terminal has a
Terminal ID
. When the RF Terminal powers up, it
asks if you want to
SIGN ON?
Pressing YES at the
SIGN ON?
prompt
causes the RF Terminal to transmit it’s
Terminal ID
and a byte of data
indi-
cating to the Base Station that it wants to sign on to the system.
When you press YES to the
SIGN ON
prompt on the RF Terminal, the
Terminal will display the following message:
WAITING ON BASE TO ACKNOWLEDGE
This message is normal when first establishing communication and may
occur occasionally during normal operation.
When the Base Station receives a
SIGN ON
message from a RF Terminal,
the Base Station transmits the SIGN ON information to the host computer.
The host computer application can then do one of two things:
1. If it has something for the Terminal to do, it can send a prompt to the
Base, which in turn transmits it to the Terminal. The RF Terminal
receives the prompt, waits for the operator to enter the requested
data, and then transmits the data back to the Base Station.
2. If the host program does nothing within an allotted time, the
Terminal displays the message:
WAITING ON HOST PROMPT
Lets suppose that a RF Terminal and a Base Station have been processing
data by sending prompts and data back and forth as described in example 1.
The Base Station sends a data prompt to the RF Terminal, the RF Terminal
transmits the operator-entered data back to the Base Station. If the host
program has another prompt for the terminal, the Base sends it out, repeat-
ing the process above.
Suppose the host program does
not
have a prompt ready to send back to the
Terminal; the Terminal transmits its data to the Base Station but does not
receive a new data prompt. The Terminal then retransmits its data (it thinks
maybe the host didn’t receive it) and waits for a response.
Once the terminal has received a prompt back from the host, the time it took
the host to respond is sent to the Terminal. For all subsequent transmissions,
