Slave Clock Mode - Mode 5; Loopback Clock For Slave Mode; Asynchronous Mode - Mode 6 - Canoga Perkins 2240 User Manual

3.4 Slave Clock Mode - Mode 5

The Slave Clock Mode is used to provide a clock to the DTE which is identical to the
clock received from the other modem. In this mode, the clock signal received from the
other end of the link is sent to the DTE on both Receive Timing (RT) and Send Timing
(ST) or equivalent signal leads. This mode is typically used in tail circuits where the
user's DCE normally provides both the transmit and receive clocks to the DTE.
Since modems operating in Slave Mode get the transmit clock from the optical input,
the clock to the DTE is only present when a valid optical signal is present (see Figure
3-2). See Figure 3-3 for a diagram of the null cable for the DCE-DCE crossover cable.

3.4.1 Loopback Clock for Slave Mode

Select a rate from the Group 1 Internal Clock Rates and set the Rate Switches accord-
ingly. Whenever a loopback is active, that clock will be sent to the DTE on the Send
Timing (ST) and Receive Timing (RT), or equivalent, signal leads.
NOTE: If the local loopback modem is operating in Mode 5 (slave clock
mode), the remote device will receive garbled data because of the overall
timing configuration. The local loopback will function correctly.

3.5 Asynchronous Mode - Mode 6

The Asynchronous Mode should be used when a data signal is present without a
separate clock signal. The only exception to this is when the signal is bipolar T1 or E1.
For those signals, the 2240 interface extracts a clock from the signal.
This mode samples the data signal at 4.096 MHz which results in a pulse distortion of
244 ns. The effect of this distortion on the connected equipment must be carefully
assessed.
For a 37% distortion limit, the maximum data rate is 1.544 Mbps for all forms of NRZ
coding. For the various forms of Manchester or Biphase coding, the limit is 768 kbps.
If the distortion limit is 25%, these limits are reduced to 1.024 Mbps and 512 kbps,
respectively.
The Rate Switches do not have any function in asynchronous mode.
2240 Fiber Optic Modem
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