How the One-Way RF System works

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, 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 either a “go to sleep” message or a new data prompt. After each delays, 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 of 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, displaying 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).