Reset Control
84
SPRUH22I – April 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
System Control and Interrupts
Table 1-4. Device Bring-Up Time Line
Time Line
Master Subsystem
Control Subsystem
Analog Subsystem/ACIB
T0
POR indicates that device is not yet
fully powered and is in reset
POR indicates that device is not yet
fully powered and is in reset
POR indicates that device is not yet
fully powered and is in reset
T1
Master subsystem out of reset. Device
Specific initialization as mentioned in
the Boot ROM guide.
Control subsystem held in reset
Analog subsystem/ACIB held in reset
T2
Bring control subsystem out of reset
Control subsystem starts executing C-
Boot ROM
Analog subsystem/ACIB held in reset
T3
Bring ACIB out of reset
T4
Master bootROM boots the device
based on the boot mode GPIO
configuration.
After system initialization, the C28x
CPU goes to IDLE mode; wakes up on
IPC interrupts
Analog subsystem/ACIB out of reset
and analog peripherals are accessible
for both master and control
subsystems.
T5
Running application on master
Master Application decides how to run
application on control subsystem.
ACIB and analog peripherals ready to
be configured, controlled and
monitored by control subsystem
application and master subsystem
application.
Below are the details on each reset source.
1.3.1.1
Power-on Reset (POR):
The Analog and Digital Subsystems' each have a Power-On-Reset (POR) circuit that creates a clean reset
throughout the device enabling glitchless GPIOs during the power-on procedure. The POR function keeps
both ARS and XRS driven low during device power up. Whenever the device is reset by a POR condition,
bit 1 of the MRESC register is set indicating that the POR has caused a reset, and because a POR reset
pulls the XRS pin low, bit 0 is also set.
NOTE:
The power-on reset also resets the JTAG controller.
While in most applications, the POR generated reset has a long enough duration to also reset other
system ICs, some applications may require a longer lasting pulse. In these cases, the ARS and XRS reset
pins (which are open-drain) can also be driven low to match the time the device is held in a reset state
with the rest of the system.
When the device is reset by a POR condition, the master subsystem begins executing the master Boot
ROM and brings the control subsystem and analog subsystem out of reset. Once out of reset, the control
subsystem starts executing its code in C-Boot ROM. Please refer to the
Boot ROM
chapter for how both
the master subsystem boot ROM and control subsystem boot ROM handle this reset cause.
1.3.1.2
External Reset Input
There are two external reset input pins on the device: XRS and ARS.
The XRS and ARS pins both respond to an external reset signal (active low), and can also drive the reset
signal out of the chip to external circuitry whenever any of the internal digital or analog subsystem resets
become active, as shown in the
. The internal resets which pull XRS low are caused by the
master subsystem watchdog modules (WDT0, WDT1 and MNMIWD). Whenever the master subsystem is
reset by an XRS condition, it will hold both control and analog subsystems in reset and bit 0 of the
MRESC register will be set to indicate an XRS caused the reset. When the device is out of reset, the
master subsystem Boot ROM will start executing and it will bring both control and analog systems out of
reset. Once out of reset, the control subsystem will start executing its own Boot ROM. Please refer to the
Boot ROM
chapter for how both the master and control boot ROMs handle an XRS reset.
It is recommended to connect both XRS and ARS pins together externally using a single trace.
The internal reset which can pull ARS low is caused by the power-on reset (POR).