Specifications

2240 Fiber Optic Modem
33
Table 3-D.
Group 4 Internal
Clock Rate Divide
Ratio
3.3.1 Standard Internal Clock Rates (Groups 1, 2 and 3)
If the data rate appears in Table 3-C, select the corresponding internal clock group with
the mode switches (refer to Table 3-A). Then set the Rate Switches to complete the rate
selection process.
3.3.2 Custom Internal Clock Rates (Group 4)
The Group 4 Internal Clock Mode can be used if an oscillator has been specified or
installed in the custom oscillator socket (refer to Section 2.1.6). The available
oscillators and their respective clock frequencies are given in Table 3-E. If the rate
appears in table, choose the appropriate oscillator option for the modem.
Obtaining the desired divide ratio may require changing the position of the TBL /
NORM DIP switch as shown in Table 3-D. The location of the TBL / NORM switch
is shown in Figures 2-3 and 3-4.
In Group 4, the Rate Switches select the divider ratio for this oscillator. Refer to
Table 3-D and Section 3.3.2 for more details.
DIP Switches
(C) Closed (O) Open
Group 4 Divide Ratios
Rate Switches Normal and Alternate Table
Rate 1 2 3 4 NORM (ON) * TBL (OFF)
0 CCCC 4 16
1 OCCC 8 32
2COCC16 64
3 OOCC 32 128
4 CCOC 48 768
5 O C O C 96 1536
6 C O O C 192 3072
7 OOOC 384 6144
8 CCCO 64 256
9 O C C O 128 512
* Factory setting