Functional Description
196
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
System Control
Table 4-1. Reset Sources (continued)
Reset Source
Core Reset?
JTAG Reset?
On-Chip Peripherals
Reset?
(1)
Programmable on a module-by-module basis by using the individual peripheral Software Reset registers starting at system
control offset 0x500.
Software peripheral reset
No
Pin configuration only
Yes
(1)
Watchdog POR
Yes
Pin configuration only
Yes
Watchdog system reset
Yes
Pin configuration only
Yes
HIB module POR
Yes
Pin configuration only
Yes
HIB module system reset
Yes
Pin configuration only
Yes
HSSR reset
Yes
Pin configuration only
Yes
MOSC failure reset
Yes
Pin configuration only
Yes
After a reset, the Reset Cause (RESC) register is set with the reset cause. The bits in this register are
sticky and maintain their state across multiple reset sequences. A bit in the RESC register can be cleared
by writing 0.
4.1.2.2
Boot Configuration
After POR and device initialization occurs, the hardware loads the stack pointer from either flash or ROM
based on the presence of an application in flash and the state of the EN bit in the BOOTCFG register. If
the flash address 0x0000.0004 contains an erased word (value 0xFFFF.FFFF) or the EN bit is of the
BOOTCFG register is clear, the stack pointer and reset vector pointer are loaded from ROM at address
0x0100.0000 and 0x0100.0004, respectively. The bootloader executes and configures the available boot
slave interfaces and waits for a programmer, host PC or boot server to load its software. The bootloader
uses a simple packet interface to provide synchronous communication with the device for I
2
C, SSI, and
UART. The speed of the bootloader is determined by the frequency of the internal oscillator (PIOSC) or
external crystal (if connected).
If the flash at address 0x0000.0004 contains a valid reset vector value and the BOOTCFG register does
not indicate the bootloader, the boot sequence causes the stack pointer and reset vector fetch from flash.
This application stack pointer and reset vector is loaded and the processor executes the application
directly.
NOTE:
If the device fails the initialization phase, it toggles the TDO output pin to indicate that the
device is not executing. This feature is provided for debug purposes.
4.1.2.3
Externally Generated POR
NOTE:
The JTAG controller can be reset by a POR or by holding the TMS pin high for 5 clock
cycles.
During an externally generated POR, the internal POR circuit monitors the power supply voltage (V
DD
) and
generates a reset signal to all of the internal logic including JTAG when the power supply ramp reaches a
threshold value (V
POR
). Reset does not complete if specific voltage parameters are not met as defined in
the device-specific data sheet. For applications that require the use of an external reset signal to hold the
microcontroller in reset longer than the internal POR, the RST input may be used as discussed in
. Holding this pin active can keep the initialization process from starting even though a
POR has occurred. This is useful for in-circuit testing and other situations where it is desirable to delay the
operation of the device until an external supervisor has released.
The POR sequence is:
1. The microcontroller waits for internal POR to go inactive.
2. The internal reset is released and the core executes a full initialization of the device.
3. When initialization is complete, the core loads from memory the initial stack pointer, the initial program
counter, and the first instruction designated by the program counter.