ZyXEL Communications U-90E, Руководство пользователя

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U-90E Data/Fax Modem
Synchronous Mode Operation
8-2
8.2 Clock Options
Synchronous data must be transmitted and received with a clock. You can choose from
three types of transmission clock sources: internal clock, external clock and slave clock.
The internal clock is the one suitable for most applications and is the default. In this case,
the clock signal is generated by the modem itself and sent to the DTE. The external clock
is the one in which the clock signal is provided by the DTE and sent to the modem. The
slave clock is used when in remote digital loopback mode. Here the recovered clock
signal from the received carrier serves as the transmission clock.
Table 8-2 Clock Options
AT-Command Description
AT&X0 * Modem provides synchronous transmit clock signal (Internal
clock to pin 15 of EIA-232D)
AT&X1 Terminal provides synchronous transmit clock signal
(External clock from pin 24 of EIA-232D)
AT&X2 Received carrier provides synchronous transmit clock signal
(Remote or Slave clock to pin 15 of EIA-232D)
In some special application (such as DNN), the received clock must be the same as
external transmission clock. In this case, you must set
s58.5 to 1 to let the received clock
lock with external clock.
8.3 Half-Duplex operation
For a half-duplex modem, the carrier only exists in one direction at any specific time. The
are two kind of half-duplex mode provided by U-90E.