Optelecom 9522A Installation And Operation Manual page 24

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DDITIONAL EATURES
In addition to the features already described the following features of operation are incorporated as either
basic indispensable functions or as performance enhancements or options.
Data Input Anti-Streaming
The electrical side anti-streaming feature, when enabled, limits the time that a terminal unit may accept and
transmit RS232 input data with a single request-to-send (RTS) enable. This feature acts independently on
both the Primary and Secondary ports and is designed to prevent a terminal unit from monopolizing the
network if a terminal unit fails in a mode causing continuous transmission. When the RTS (or RTSE) input to a
port is set high (TRUE), the RS232 side anti-streaming counter is armed. When data transmission begins the
timer begins, allowing the terminal to transmit data for a period of time up to the time-out limit. When the
terminal unit stops transmitting it must immediately set the RTS (or RTSE) input low (FALSE), resetting the
timer. If the terminal continues to transmit data to the modem past the timeout period, the transmission from
the modem will cease, the CTS (or CTSE) output will go low, the specific FAULT indicator will illuminate, and
the dry contact relay ALARM will activate. To use this feature, an active RTS (or RTSE) input signal is required.
If the RTS input cannot be actively controlled, the RS232 side anti-streaming feature must be disabled. S2
switch numbers 1, 2, and 3 allow the user to select the timeout period or disable the feature. If the feature is
disabled, RTS (and RTSE) inputs will be internally enabled, eliminating the need for the user to connect to the
RTS (or RTSE) input pins. To select a timeout, calculate the longest transmission burst expected by the
terminal and pick the next highest timeout period. If this is not practical in your system, just disable it. NOTE:
Enabling this feature sets the modem to ONLY transmit on the fiber data presented to the I/O ports when RTS
in active. This means that the source of the RTS signal must be actively controlled and not just held active. It
must go inactive when not transmitting data to reset the timer. For this reason, it cannot be used in
connecting one modem to another in a branch off of a daisy chain, as there is no way to control the RTS input.
Optical Anti-Streaming
The optical side anti-streaming feature, when enabled, disconnects an optical receiver from the circuit in the
event that the receiver's output goes high for a period longer than would be expected in normal data flow.
This may occur due to a receiver, transmitter, or terminal equipment failure. A failure of this type could
disable one modem, part of the network, or the whole network, depending on the network architecture, if it
were not for the optical anti-streaming circuitry. The circuit works as follows: As long as the data is high
(optical power present at the receiver) the timeout proceeds. Whenever the data goes low, as it does for all
normal zeros, the timeout resets. As long as the data does not contain a long string of continuous ones that
exceeds the timeout period, the anti-streaming will not be triggered. If there are too many ones in a row or if
there is a failure that leaves the receiver output constantly high, the receiver output will be disconnected from
the circuit and the FAULT indicator will illuminate. The optical anti-streaming timeout is approximately 70
milliseconds, sufficient for ASCII character transmission down to about 150 baud.
Clear to Send Inhibited by Optical Side Activity
Another optional feature, enabled or disabled by S2 switch number 6, causes the disabling of the Clear-to-
Send (CTS or CTSE) control line output and the output data (RD or RDE) in the presence of fiber side data
activity. Normally, the system software will preclude such an occurrence, but as a safeguard this feature will
prevent a terminal from interfering with data already traveling on the optical trunk or ring either from the
master or from another terminal. The circuit uses the "Priority Select" timers to determine the CTS disable
period. The selected Priority Select timeout applies. The selected rates should be sufficient to keep CTS
disabled for a period of one byte. For ASCII character transmission at rates below 600 baud, this feature
should not be used.
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