MCP2021/2
1.5.8
FAULT/TXE
Fault Detect output and Transmitter Enable input
bidirectional pin.
This pin is an open-drain output. Its state is defined as
shown in
The transmitter driver is disabled
whenever this pin is low (‘0’), either from an internal
fault condition or by external drive. This allows the
transmitter to be placed in an off state and still allow the
voltage regulator to operate. Refer to
The FAULT/TXE also signals a mismatch between the
TXD input and the L
BUS
level. This can be used to
detect a bus contention. Since the bus exhibits a
propagation delay, the sampling of the internal
compare is debounced to eliminate false faults.
This pin has an internal
approximately 750 kΩ.
pull-up
resistor
of
Note 1:
The FAULT/TXE pin is true (0) whenever
the internal circuits have detected a short
or thermal excursion and have disabled
the L
BUS
output driver.
2:
FAULT/TXE is true (0) when V
REG
not OK
and has disabled the L
BUS
output driver.
The FAULT/TXE pin sampled at a rate faster than every
10 µs.
TABLE 1-2:
TXD
In
L
H
L
H
x
x
RXD
Out
H
H
L
L
x
x
FAULT/TXE TRUTH TABLE
FAULT/TXE
LIN
BUS
I/O
V
BB
V
BB
GND
GND
V
BB
V
BB
Thermal
Override
OFF
OFF
OFF
OFF
ON
x
External
Input
H
H
H
H
H
L
Driven
Output
L
H
H
H
L
x
Definition
FAULT,
TXD driven low, LIN
BUS
shorted to
V
BB
OK
OK
OK,
data is being received from the LIN
BUS
FAULT,
Tranceiver in thermal shutdown
NO FAULT,
the CPU is commanding the
tranceiver to turn off the transmitter driver
Legend:
x = don’t care
Note 1:
The FAULT/TXE is valid after approximately 25 µs after TXD falling edge. This is to eliminate false fault
reporting during bus propagation delays.
1.5.9
RESET
RESET is an open-drain output pin. This pin tracks an
internal signal that tracks the internal system voltage
has reached a valid, stable level. As long as the internal
voltage is valid, this pin will remain high (‘1’). When the
system voltage drops below the minimum required, the
voltage regulator will shut down and immediately
convert the RESET output to (‘0’). When connected to
a micro-controller input, this can provide a warning that
the voltage regulator is shutting down (see
Alternately, it can act as an external brown-out by
connecting the RESET output to MCLR (see
voltage, RESET is asserted immediately upon entering
the Powerdown mode.
©
2009 Microchip Technology Inc.
DS22018E-page 9
MICROCHIP [ MICROCHIP TECHNOLOGY ]
