LM3S3749 Luminary Micro, Inc, LM3S3749 Datasheet - Page 67

• Manufacturer Part Number: LM3S3749
• Description: Lm3s3749 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

6.1.2.3
6.1.2.4
June 02, 2008
2.
The external reset timing is shown in Figure 24-9 on page 701.
Power-On Reset (POR)
The Power-On Reset (POR) circuit monitors the power supply voltage (V
generates a reset signal to the internal logic when the power supply ramp reaches a threshold value
(V
supply (V
The device must be operating within the specified operating parameters at the point when the on-chip
power-on reset pulse is complete. The 3.3-V power supply to the device must reach 3.0 V within
10 msec of it crossing 2.0 V to guarantee proper operation. For applications that require the use of
an external reset to hold the device in reset longer than the internal POR, the RST input may be
used with the circuit as shown in Figure 6-1 on page 67.
Figure 6-1. External Circuitry to Extend Reset
The R
the RST input. The diode (D
The Power-On Reset sequence is as follows:
1.
2.
The internal POR is only active on the initial power-up of the controller. The Power-On Reset timing
is shown in Figure 24-10 on page 702.
Note:
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 the power supply (V
below a brown-out threshold voltage (V
generate a controller interrupt or a system reset.
TH
The internal reset is released and the core loads from memory the initial stack pointer, the initial
program counter, the first instruction designated by the program counter, and begins execution.
A few clocks cycles from RST de-assertion to the start of the reset sequence is necessary for
synchronization.
The controller waits for the later of external reset (RST) or internal POR to go inactive.
The internal reset is released and the core loads from memory the initial stack pointer, the initial
program counter, the first instruction designated by the program counter, and begins execution.
D
). If the application only uses the POR circuit, the RST input needs to be connected to the power
1
1
and C
The power-on reset also resets the JTAG controller. An external reset does not.
DD
R
) through a pull-up resistor (1K to 10K Ω).
C
1
1
1
components define the power-on delay. The R
R
2
RST
1
) discharges C
Stellaris
Preliminary
BTH
). If a brown-out condition is detected, the system may
1
rapidly when the power supply is turned off.
2
resistor mitigates any leakage from
LM3S3749 Microcontroller
DD
). The POR circuit
DD
) drops
67