CANOGA PERKINS 2270 Fiber Optic Modem - Manual (Page 18)

18
Canoga Perkins
The outside case of the DC-powered modems will run warmer to the touch than the corresponding
AC-powered units. This is because the cover is used as a heat sink for the DC/DC converter.
2.6 Rack Chassis Installation
The 2201 Rack Chassis is designed to accommodate up to ten 2270 modems; see Figure 2-2.
The 2201 will fit into a standard 19-inch equipment rack. Tabs are provided on each side of the unit
and are predrilled for standard spacing. For further details, refer to the 2201 Rack Chassis
User Manual.
2.7 Mode and Rate Selection
NOTE: The switch notation standard for mode and rate is the following: Closed = ON,
Open = OFF.
The 2270 has three basic clock operating modes: External, Internal and Slave. These allow the
modem, in combination with the Internal Polarity Option jumper, to be configure for a wide range of
applications.
Asynchronous operation is accomplished by setting the modem to Internal Mode and oversampling
the data (refer to Section 2.7.2, "Internal Clock Operation").
The operating mode is selected by setting positions 4, 5 and 6 of the eight-section switch bank on
the front panel. Table 2-A lists the modes and the switch positions. The switch positions are
numbered from left to right (1 to 8).
2.7.1 External Clock Operation
The modem can be set to accept an external clock by closing switch position 4 of the switch block
on the front panel. Leaving switch positions 5 and 6 open will ensure that the transmit clock output
is clamped.
2.7.2 Internal Clock Operation
The modem can be set to provide an oscillator-derived clock to the DTE by closing switch position
6 of the eight-section switch bank on the front panel. Switch position 5 must be left open. Refer to
Section 2.7.4 for information on Data Rates. Refer to Section 2.7.7 regarding switch position 4.
NOTE: For SCT Polarity, refer to Figure 1-3 and Table 1-E; refer to Section 2.7.7 for "Con-
sideration of Propagation Delays."