CANOGA PERKINS 2270 Fiber Optic Modem - Manual (Page 26)

26
Canoga Perkins
3.4 Programmable Buffered ECL Interface / Model
ECL
This interface uses standard 10KH ECL (biased to -5.2V) to allow operation over 110 ohm twisted
pair cable up to a maximum speed of 20 Mbps. The maximum cable length recommended is 25
feet.
This interface is identical to the Model P53, described in Section 3.9, with the following excep-
tions:
1. The pin numbering of the J3 wire wrap header is different. Note however that the pin assign-
ments for the interface connectors J1 and J2 are the same as those for the Model P53. See
Figure 3-2.
2. The electrical characteristics for the 10KHECL differential signals are as follows:
•
Input z - 100
Ω
±10%
•
Output z - 50
Ω
±10%
•
Output Voltage Swing:
-0.9 ±10% VDC and -1.75 ±5% VDC
The delay line values are shown in Table 3-E.
This interface is typically used to interface with the RED (clear) side of data encryption equipment
such as the KG-95. In these applications the interface acts as a "tail-circuit adapter" device. This
configuration allows the modem to accept TWO synchronous clocks (typically, DCE devices only
accept one); one for transmit (external clock) and one for receive (FIFO output clock).
Another common application is with systems that communicate over geosynchronous satellites.
In this application, the FIFO makes up for clock drift (doppler shift) caused by the satellite's
elliptical orbit around the earth.
The FIFO allows the user to recondition either the received or transmitted data (not both). The
delay line, in conjunction with a four-position DIP switch, provides an option for fine-tuning the
relationship between clock and data timing in a range of from 20 to 170 nanoseconds in steps of
10 nanoseconds.