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THEORY OF OPERATION
4.1 INTRODUCTION
Basic operation of the Model F22XX is similar to a two-channel, full duplex multiplexer.
The first channel is used for high-speed synchronous data. The second channel is used for
transmit clock, or for an asynchronous second data channel. Both channels may be used for low-
speed (less than 100 Kbps), asynchronous operation.
The first of the three operating modes of the F22XX Modems permits data transparency.
In the Automatic mode a data rate from 250 Bps to 10 Mbps is accepted and the data rate may be
variable, as is sometimes seen in high-speed telemetry systems. An internal bit rate monitor
circuit selects the source of the transmit clock. At clock rates of less than 100 Kbps, or when no
external clock is present, an internal 10 MHz reference signal is utilized as the clock. This
assures a sufficiently large number of samples for minimum end-to-end timing jitter. The actual
clock signal is used at clock frequencies greater than 100 kHz.
If a fully transparent synchronous link is not required, the clock and control paths may be
used as additional asynchronous data paths. The transmit and receive clock inputs will handle
data rates from 0 to 76.8 Kbps asynchronously.
SECTION 5
MAINTENANCE AND TROUBLESHOOTING