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Lets suppose that a RF Terminal and a Base Station have been processing data by sending prompts and data back and forth as de-
scribed 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, repeating 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, the terminal goes to sleep until the time it took the last time for the host to respond has expired; then
the terminal wakes up and listens. If it has nothing, it retransmits its data and waits for a response.
The original data transmission could have collided with another message, or the Base could have received the Terminal's data but
had not yet received the host's prompt response. If the previous transmission got through, the Base Station knows that the data is a
retransmission rather than a new data transmission so it sends a message to the Terminal telling it:
“I have nothing for you from the host, go to sleep”.
While in “sleep” mode, the Terminal “wakes” up at a random interval and asks “do you have anything for me yet”, waiting for ei-
ther a “go to sleep” message or a new data prompt. After each delay, the Terminal displays:
WAITING FOR HOST PROMPT
If a Terminal receives
no
response at all from a Base Station (no data prompt or “go to sleep” message), it retransmits its data and
waits for a response. If the Terminal gets no response after 10 re-transmissions, it assumes it is out of range from the Base Station
with which it was communicating, and attempts to establish contact with any Base Station. If the Terminal can't contact any Base
Station, it displays:
TRANSMISSION FAILED
HIT ANY KEY_
Pressing a key on the Terminal starts the re-transmission process over again. The RF Terminal will try to retransmit its data, dis-
playing the TRANSMISSION FAILED message after every 10 unsuccessful tries.
Can I change a prompt after it has been sent?
Normally once the Terminal has received a prompt from the host, it goes to sleep and waits (as long as it takes) for the operator to
scan or key something in response. The host cannot send another prompt without creating a "Sequence Error." You might want to
change the prompt or locate a lost terminal with beeping.
There is a special setting in the RF Terminal Setup in which you specify the time (between 5 seconds and 7 minutes) you want the
Terminal to quit waiting for input from the operator, blank the screen, send back a special control character to the host program,
display "Waiting on Host Prompt" and wait for a prompt from the host application program; the host application program can
choose to send back different instructions or simply repeat the previous prompt's instructions, (See
Automatic Check Back
in the
Programming Section
).
How the One-Way RF System works
The RF System can be used to perform “dumb” data entry to the computer – you could even use
PortKey
to transmit the data through
a serial connected Base as though it has been entered from the keyboard. This is useful if you want to enter data directly into an ap-
plication. This type of data transmission is called
One-Way Mode
. Once the RF Terminal transmits data to the Base Station, the
Base Station acknowledges receipt of the information by echoing back the data to the Terminal that sent it, along with a beep. If the
data transmission
did not
make it through to the Base station after 10 tries, the RF Terminal will give two long beeps and display the
following message:
TRANSMISSION FAILED
TO RETRY, MOVE CLOSER
AND PRESS ENTER.
F1 TO EXIT.
Содержание 7100 RF Terminal Series
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