Reset Control
85
SPRUH22I – April 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
System Control and Interrupts
1.3.1.3
TRST
TRST is a JTAG test reset with an internal pulldown, and when driven high, gives the scan system control
of the operations of the device. If this signal is not connected or driven low, the device operates in
functional mode, and the test reset signals are ignored. TRST resets the JTAG TAPs of both the master
subsystem CPU and control subsystem CPU.
NOTE:
TRST is an active-high test pin and must be maintained low during normal device operation.
The TRST reset does not show up on XRS. Note that TRST is different from a debugger reset. The
debugger reset on the Cortex-M3 is realized by writing to the NVIC registers and on the C28x CPU it is
realized by writing to TI-internal hidden registers.
1.3.1.4
Watchdog Timer 0,1 Reset
This device has two watchdog timer modules on the master subsystem in case one watchdog clock
source fails. Watchdog Timer 0 is run off the system clock and Watchdog Timer 1 is run off the main
oscillator. Each module operates in the same manner except that because the Watchdog Timer 1 module
is in a different clock domain, register accesses must have a time delay between them. The watchdog
timer can be configured to generate an interrupt to the microcontroller on its first time-out and to generate
a reset on its second time-out.
After the watchdog's first time-out event, the 32-bit watchdog counter is reloaded with the value of the
Watchdog Timer Load (WDTLOAD) register and resumes counting down from that value. If the timer
counts down to zero again before the first time-out interrupt is cleared, and the reset signal has been
enabled, the watchdog timer asserts its reset signal to the microcontroller. The watchdog timer reset
sequence is as follows:
1. The watchdog timer times out for the second time without being serviced.
2. An internal reset is asserted which pulls XRS low and this resets the whole device and appropriate bits
in the MRESC register are set.
Note that on this device, the watchdogs are available only on the master subsystem. The control
subsystem does not have its own watchdog, but when the master subsystem watchdogs generate a reset,
it will reset the entire device.
When the device is out of reset, the master subsystem boot ROM will start executing and it will bring both
the control and analog subsystems out of reset. Once out of reset, the control subsystem will start
executing its own boot ROM. Refer to the
Boot ROM
chapter for more details on how the master
subsystem and control subsystem boot ROM handles watchdog timer resets.
1.3.1.5
Master NMI Watchdog Timer Reset
This device has a watchdog timer associated with its NMI logic, which when an enabled non-maskable
interrupt is generated to the CPU, the NMIWD timer starts counting. The NMIWD will then generate a
reset if the MNMIWDCNT counter register value reaches the value programmed in the MNMIWDPRD
period register. Once the MNMIWD counter starts counting, it will stop and reset to 0 only if all the flags in
the MNMIFLG register are cleared.
Note that the ACIBERR NMI is disabled on reset, and if the application software does not enable this NMI
by setting bit 9 in the MNMICFG register, no NMI will be triggered to the CPU if these error conditions
occur. Any other NMI condition will trigger an NMI to the CPU and the NMIWD counter will start counting.
Refer to the MNMI section in this document for more details on MNMI sources, and refer to the
Boot ROM
chapter for more details on how the master boot ROM software handles different NMIs.
Whenever an MNMIWD reset is generated, it will pull the XRS pin low. This will cause the entire device to
reset and both the analog and control subsystems will be held in reset. Once out of reset, the master
subsystem will start executing boot ROM and bring the analog and control subsystems out of reset. Once
out of reset, the control subsystem will start executing its boot ROM. Refer to the
Boot ROM
chapter for
more details on how boot ROM handles this reset.