Fail; Recommended Fail# Circuit - Intel i960 Design Manual

9.7

FAIL#

Many applications use a light emitting diode (LED) to indicate when the FAIL# pin is low (active).
However, when an
3.3 V, the LED can still be forward biased enough to glow. To ensure the LED extinguishes when
FAIL# goes high, Intel recommends the circuit shown in
The two diodes dissipate about 1.4 V, so the LED voltage drops too low to glow when the FAIL#
pin goes high. Use a low current LED that can operate at 3-5 mA. This design works whether V
is 5 V or 3.3 V nominal.
An alternative is to eliminate the diodes and power the LED from the 3.3 V V
RM/RN I/O
Figure 9-22. Recommended FAIL# Circuit
Design Guide
®
Intel 80960RM/RN Processor 5 V and 3.3 V Design Considerations
RM/RN I/O processor
processor.
80960RM/RN
FAIL#
Intel® i960® RM/RN I/O Processor
is in the design, and the FAIL# pin is high (inactive) at
Figure 9-22.
~3.1 - 4.1V
*
LED
supply of the
CC
V
CC
1N4002, or Equivalent
Ω
390 ,
10%,
0.125 W
CC
39