Transmit Timing; Internal Clock (Sct); External (Terrestrial) Clock (Scte); Loop Timing (Scr) - Advantech AMT-73 Installation And Operation Manual

Transmit Timing

3.5.1
Data can be clocked into and out of the transmit de-jitter buffer via the four clocking modes described
below:

3.5.1.1 Internal Clock (SCT)

The modem supplies the clock to the DTE device, which uses that clock to transmit the data out of its
buffer. The modem issues ST to the DTE, and the DTE device returns TT to the modem. In some
cases, the DTE does not return TT, which is acceptable for low data rates, but for higher data rates,
AdvantechAMT cannot guarantee clock/data relationships due to delays induced by varying cable
lengths.
This mode is entered by selecting IFTXCLOCK internal (SCT).

3.5.1.2 External (Terrestrial) Clock (SCTE)

The DTE device supplies the clock to the modem (TT), which uses its internal clock to transmit the data
out of its buffer. The modem uses the TT clock to 1) clock the SD into the jitter buffer, and 2)
synchronize its internal modem clock. The internal modem clock, which is smoothed, clocks the data
out of the jitter buffer, which removes the short-term jitter that may appear on the incoming data.
This mode is entered by selecting IFTXCLOCK external (SCTE).

3.5.1.3 Loop Timing (SCR)

The modem's Demod Clock supplies the clock to the DTE device, which uses that clock to transmit the
data out of its buffer. The modem issues ST to the DTE, and the DTE device returns TT to the modem.
In some cases, the DTE does not return TT, which is acceptable for low data rates, but for higher data
rates, AdvantechAMT cannot guarantee clock/data relationships due to delays induced by varying
cable lengths.
This mode is useful when the far end modem has to provide a clock to the DTE equipment, which is
now synchronized to the clock from the near end modem.
This mode is entered by selecting IFTXCLOCK rxloop (SCR).

3.5.1.4 RS530TFD Clock Recovery

This special feature is standard with the AMT-73L modem. It is a requirement that the modem extract
the internal clock from the incoming data in the absence of TT per MIL-STD-188-165A. This operates
on the RS530/EIA449 data interface.
This mode is entered by selecting IFTXCLOCK rs530tfd.

Receive Timing

3.5.2
Data can be clocked into and out of the Doppler Buffer via the four clocking modes described below:

3.5.2.1 Doppler Buffer Auto

In this mode the Modem automatically selects what is considered to be an appropriate fill level (delay)
for the Doppler buffer. This mode can be used with any of the RX Timing modes.
Note: If IFRXCLOCK is set to 'demod (SCR)' then the Doppler buffer should be configured to Manual
mode with a low fill level (32 to 100bytes) to minimize latency.
3.5.2.2 Doppler Buffer Enabled – Internal ST Clocking (SCT)
AMT-70/AMT-73/AMT-75 Installation and Operation
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