Appendix C: Wiring Diagrams Pin Assignments 87
USD Serial Cable Pin
Assignments
Bi-phase/Tach/GPI/Pilot
Port Interfacing Notes
◆ The six opto-isolators are 6N137 devices.
Each port input passes through a 390 ohm
series resistor to the cathode. Each port re-
turn comes directly from the anode. The bi-
phase/tach inputs share the same return.
◆ The two TTL-level GPI outputs are driven
by a 74FCT541. Each output passes
through a 220 ohm series resistor.
◆ The fuse is thermally activated. The cur-
rent rating varies between 1.0 A at 60˚C
and 1.5 A at 20˚C. The time to trip varies
with temperature and current. The typical
time to trip at 1.5 A is 5 minutes. Time to
trip at 8 A is 5 seconds. After tripping, the
fuse will return to its low-resistance state
when the current is reduced sufficiently.
15
PILOT_IN- Pilot tone input, negative
16
PILOT_IN+ Pilot tone input, positive
17
RET0 Return from GPI opto-isolator “0”
18
GPIN0 Input to GPI opto-isolator “0”
19
RET1 Return from GPI opto-isolator “1”
20
GPIN1 Input to GPI opto-isolator “1”
21
RET2 Return from GPI opto-isolator “2”
22
GPIN2 Input to GPI opto-isolator “2”
23
RET3 Return from GPI opto-isolator “3”
24
GPIN3 Input to GPI opto-isolator “3”
25
VDD +5V DC, fuse protected (see notes below)
Shell
GND Connected to chassis ground
Connector Pin Assignments
Mini DIN 8-pin Male to Mini
DIN 8-pin Male
12
21
35
44
53
68
77
86
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