Bell 5902 - Anti-Streaming; Soft Carrier Turn-Off

5902 Bell 202 Modem Hardware Manual
October 19, 2007
20
4.5.3.3 Effect of Soft Carrier Turn-off Tones
Reception of a soft carrier turn-off tone ends reception within the soft carrier turn-off detect time
(see Specifications). The carrier loss delay is not used. The modem de-asserts the DCD output and
turns off the CD LED when the SCT tone is received.
4.5.4 Anti-Streaming
The AS0 and AS1 switches control the anti-streaming option. There are four settings.
ANTI-STREAMING
TIME
NONE
10 s
30 s
60 s
AS0 switch
open
closed
open
closed
AS1 switch
open
open
closed
closed
The anti-streaming time determines the maximum time a modem can continuously transmit. This
prevents a DTE from disabling a radio network or multi-drop line by transmitting data continuously.
If the DTE transmits longer than the anti-streaming time, the modem turns off the KEY output, and
de-asserts the CTS and DCD signals to the DTE. The modem remains in this state until the DTE de-
asserts RTS. The modem returns to normal operation once RTS is de-asserted.
Anti-streaming is active only when the modem is configured for half duplex operation. It ignores
anti-streaming in full duplex operation.
4.5.5 Soft Carrier Turn-off
Switches SC0 and SC1 control the length of the soft carrier turn-off (SCT) tone. There are four
options.
SCT Tone Length
(+/– 1 ms)
No
Tone
13 ms
25 ms
38 ms
SC0 switch
open
closed
open
closed
SC1 switch
open
open
closed
closed
The modem can transmit a soft carrier turn-off (SCT) tone to inform receiving modems to turn off
their receivers. The tone is transmitted at the end of a transmission. It prevents the receivers from
detecting a noise burst at the conclusion of each transmission
The tone can be disabled if the receiving modem does not recognize the SCT tone.
The modem de-asserts the CTS signal when transmitting the SCT tone. An asserted RTS signal will
not be recognized until the SCT time has concluded.
Half duplex and two wire applications should use the shortest functional (non-zero) SCT tone, to get
the quickest turn around time possible. The modem will not transmit while the SCT tone is being
received.
4.5.5.1 Soft Carrier Turn-off Reception
The modem always recognizes the soft carrier turn-off tone, regardless of the SCT settings.
Reception of a soft carrier turn-off tone always ends reception within the soft carrier turn-off delay
time (see Specifications). The carrier loss delay is not used when a soft carrier turn-off tone is
detected.