User manual

43
2270 Fiber Optic Modem
Table 3-M. Jumper Strap Options
JUMPER DESCRIPTION FACTORY CONFIGURATION
ID TW TW8 T22 T88 D22 D88
W1/W2 Defines whether alarm relay W2 W2 N/A N/A N/A N/A
contact is normally open (W2)
or normally closed (W1)
W3/W4* W3=VCO disabled W4 W4 W4 W4 W4 W4
W4=VCO enabled
W5/W6 W6=Normal SCT W6 W6 W6 W6 W6 W6
W5=Inverted SCT
W7/W8 W7=Shield connected toW7 W7 W7 W7 W7 W7 W7
chassis ground
W8=Shield connected to
signal ground
W9/W10 W9=Chassis ground con- W10 W10 W10 W10 W10 W10
nected to signal ground
W10=Not connected
E2 TxD RCV termination resistor N/A I N N/A I N N/A I N
center tap to shield ground
E3 SCTE RCV termination resistor N/A I N N/A I N N/A I N
center tap to shield ground
* 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.
3.9.1 Model -TW
The signaling used on this interface is RS-422A. Four TwinAx connectors (BJ-77 type) are used
for the physical connection (see Figure 3-11).
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.
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.