CANOGA PERKINS 2240 Fiber Optic Modem - Manual (Page 25)

2240 Fiber Optic Modem
25
2.2.2.2 Internal Clock Option Switches
There are two switches on the Internal switch block which affect the operation of
the Clock circuits:
•
TBL / NORM
•
CLK / EXT
2.2.2.2.1 TBL / NORM Switch
The TBL / NORM switch controls the Data Rate Table as indicated in Table 3-D.
It is configured as ON when shipped from the factory. If it is switched to OFF,
the alternate Divide Ratios become active.
Factory Setting = ON
2.2.2.2.2 CLK / EXT Switch
The CLK / EXT switch controls which clock is used for synchronous input. If it is
switched to ON, any mode which sources Send Timing (Internal or Slave) will use a
turned-around clock coming in on Terminal Timing from the user's equipment. This
compensates for round-trip delays in the sourced clock which could otherwise shift
the clock-data phasing of the transmit signal and cause errors. This setting can
only be used where leads for both are available, and if the user's equipment can
turn the Send Timing back around onto the Terminal Timing leads, either internally
or at the other end of the cable.
Factory Setting = OFF