LM3S818 Luminary Micro, Inc, LM3S818 Datasheet - Page 51

• Manufacturer Part Number: LM3S818
• Description: Lm3s818 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

6.1.2.3
6.1.2.4
February 6, 2007
3.
The external reset timing is shown in Figure 20-8 on page 383.
Power-On Reset (POR)
The Power-On Reset (POR) circuitry detects a rise in power-supply voltage and generates an
on-chip reset pulse. To use the on-chip circuitry, the RST input needs a pull-up resistor (1K to
10K Ω).
The device must be operating within the specified operating parameters at the point when the
on-chip power-on reset pulse is complete. The specified operating parameters include supply
voltage, frequency, temperature, and so on. If the operating conditions are not met at the point of
POR end, the Stellaris controller does not operate correctly. In this case, the reset must be
extended using external circuitry. The RST input may be used with the circuit as shown in
Figure 6-1.
Figure 6-1. External Circuitry to Extend Reset
The R
the RST input. The diode discharges C
The Power-On Reset sequence is as follows:
1.
2.
3.
The internal POR is only active on the initial power-up of the controller. The Power-On Reset
timing is shown in Figure 20-9 on page 383.
Brown-Out Reset (BOR)
A drop in the input voltage resulting in the assertion of the internal brown-out detector can be used
to reset the controller. This is initially disabled and may be enabled by software.
The system provides a brown-out detection circuit that triggers if V
circuit is provided to guard against improper operation of logic and peripherals that operate off V
and not the LDO voltage. If a brown-out condition is detected, the system may generate a
controller interrupt or a system reset. The BOR circuit has a digital filter that protects against
noise-related detection. This feature may be optionally enabled.
The internal reset is released and the controller fetches and loads the initial stack pointer, the
initial program counter, and the first instruction designated by the program counter, and then
begins execution.
The controller waits for the later of external reset (RST) or internal POR to go inactive.
After the resets are inactive, the main crystal oscillator must be allowed to settle and there is
an internal main oscillator counter that takes from 15-30 ms to account for this. During this
time, internal reset to the rest of the controller is held active.
The internal reset is released and the controller fetches and loads the initial stack pointer, the
initial program counter, and the first instruction designated by the program counter, and then
begins execution.
1
and C
1
components define the power-on delay. The R
D
Preliminary
1
1
rapidly when the power supply is turned off.
R
C
1
1
R
2
RST
Stellaris
2
resistor mitigates any leakage from
DD
drops below V
LM3S818 Data Sheet
BTH
. The
DD
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