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Figure 3-1.
2240 Front Panel
Mode / Rate Switches
3. Mode and Rate Selection
3.1 Operating Mode / Data Rate Selection
The 2240 has eight clock operating modes: seven modes for synchronous data
transmission and one asynchronous mode. Each synchronous mode is character-
ized by one of three transmit clock types: External Clock (clocked from customer's
equipment), Internal Clock (modem generates Tx clock and RX clock) and Slave
Clock (transmit clock same as received from far-end modem).
The operating mode is selected by setting three of the eight paddle-style switches
(positions 5, 6 and 7) on the front panel (see Figure 3-1). Table 3-A lists the modes
and the switch positions. The switch positions are numbered from left to right (1 to 8).
NOTE: Front panel DIP switch Position 8 is now functional. It acts as
an optical receiver frequency range select. OPEN selects the new low
range and CLOSED selects the original (or normal) operating range.
This switch should be in the CLOSED position except when the far
end modem is operating in Locked External Mode (Mode 7) and the
far end modem's external clock frequency falls into the LOW range
(refer to Table 3-B).
1
OPEN
CLOSED
2
3
4
5
RATE SWITCHES
(RATE 0 / MODE 7 / ORIGINAL RANGE SHOWN)
2240 Fiber Optic Modem
6
7
8
RANGE
MODE
SELECT
29
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