Long Line Driver - Control Data Corporation INFORMATION SYSTEMS TERMINAL II Hardware Maintenance Manual

I
When long line transmitter is more positive than long line
receiver, the LED will conduct and emit light, causing the
NPN phototransistor in the receiver to conduct. This, in
turn, will increase the voltage at the base of 01, turning
01 on and lowering the output (collector) to a TTL low.
When long line transmitter is equal to or lower than long
line receiver, the LED will be off and the output of 01
high.
Therefore, the data is inverted by the receiver. The diode
across the input lines prevents the LED from being reverse
biased.
The long line driver lines, when enabled, provide the
source and sink current required to match the long line
receivers. Figure 1-4 shows the typical long line driver
circuit.
">---___ - - - -.....
----~:>LONG LINE
+
01
XMIT DATA (TTL)
TI, T2, AND T3
=
RS-232-C DRIVERS (MCI488),
CDC PART NUMBER 36186400
01
=
DIODE 1 N4148, CDC PART
NUMBER 51007385
.----~~LONG LINE-
03339
Figure 1-4. Long Line Driver
These three drivers connected in parallel can drive a long
line receiver (figure 1-4) 10 000 feet (3000 metres) when
using the proper cable.
The diode prevents the long line transmitter from going
more negative than the diode forward bias drop (0.6 V),
thus protecting the receiving LED from large reverse bias
voltage.
A low TTL input to the driver will switch long line trans-
mitter to a positive voltage, driving current through the
load (receiver). This is the on state. .
1-8
82100083 B