CANOGA PERKINS 2240 Fiber Optic Modem - Manual (Page 80)

Chapter 4 Data Interfaces 2240 Fiber Optic Modem User Manual
High-Speed RS-422/Mil-Std 188-114C Interfaces
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SCT should be selected if the modem is set for Internal or Slave Clock mode.
SCTE should be selected if the modem is set for External Clock mode.
NOTE: The SCT output cannot be returned on the SCTE leads to eliminate
propagation delay problems with this interface.
4.10.2 Model TW8
The signaling used on this interface is Mil-Std 188-114C. Four TwinAx connectors (BJ-77, 3-lug)
are used for the physical connection (see Figure 4-16).
A switch is provided to select whether the fourth TwinAx (SCT/SCTE) is to be used as an output
(SCT) or as an input (SCTE). By setting the switch to the SCT position, the port becomes an
output providing the clock to the connected device. When set for SCTE, the port becomes an
input and will accept a clock from the connected device.
T22 RS-422A 5 TwinAx Figure 4-17 <100 Ohms 100 Ohms ±10%
T88 Mil-Std 188-114C 5 TwinAx Figure 4-17 <100 Ohms 78 Ohms ±10%
D22 RS-422A DC-37 Table 4-23 <100 Ohms 100 Ohms ±10%
D88 Mil-Std 188-114C DC-37 Table 4-23 <100 Ohms 124 Ohms ±10%
Table 4-22. Jumper Strap Options
Jumper ID Description
Factory Configuration
TW TW8 T22 T88 D22 D88
W3/W4* W3 = VCO disabled
W4 = VCO enabled W4 W4 W4 W4 W4 W4
W5/W6** W6 = Normal SCT
W5 = Inverted SCT W6 W6 W6 W6 W6 W6
W5/W6 W7 = Shield connected to chassis ground
W8 = Shield connected to signal ground W7 W7 W7 W7 W7 W7
W9/W10 W9 = Chassis ground connected to signal ground
W10 = Not connected W10 W10 W10 W10 W10 W10
E2 TxD RCV termination resistor N/A IN N/A IN N/A IN
E3 SCTE RCV termination resistor center tap to
shield ground N/A IN N/A IN N/A IN
* W3/W4 jumper option may not exist on some older versions. It is only required when performing Local
loopbacks. The W4 position corrects the duty cycle of External Clock above 9 Mbps.
** The W5/W6 jumper option serves the same function as the SCT Normal/Invert Jumper on the main
2240 board. Either one can be used to invert SCT. Refer to section 2.1.6 for details.
Table 4-21. Model Characteristics (Continued)
Model
Electrical Interface
Type
Physical
Interface
Type
Physical
Interface
Figure/
Table
Driver
Impedance
Termination
Impedance