CANOGA PERKINS 2240 Fiber Optic Modem - Manual (Page 87)

2240 Fiber Optic Modem
87
4.10 High-Speed RS-422 / Mil-Std 188-
114C
Interfaces
There are three High-Speed RS-422 interface models (TW, T22 and D22) and three
High-Speed Mil-Std 188-114C interface models (TW8, T88 and D88) available.
All can operate up to 20 Mbps (2240 limited to 2.048 Mbps). All support only
clock and data signals as shown in Table 4-R. Both the RS-422A and Mil-Std 188-
114C are balanced differential electrical signals.
Signal Full Name Direction
TxD Transmit Data To Modem
RxD Receive Data From Modem
SCR Serial Clock Receive From Modem
SCT Serial Clock Transmit From Modem
SCTE External Clock Transmit To Modem
Table 4-S.
TwinAx
Supported
Signals
The RS-422A operates between +1 and +4 volts whereas the Mil-Std 188-114C
swings between +/-3 volts. The termination impedances vary slightly as illustrated
in Table 4-T. The two interface types will communicate with each other but
center tap ground jumpers E2 and E3 must be removed from a Mil-Std 188-114C
interface (refer to Table 4-U).
The basic differences between the models is the type of physical connectors used
for the interface. Table 4-T lists the six interface models with the corresponding
source and termination impedances and physical connectors. Table 4-U shows the
jumper options available and the factory default settings for the jumpers.
4.10.1 Model TW
The signaling used on this interface is RS-422A. 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.