C8051F980-C-GM Datasheet, PDF (181/325 Pages) Silicon Laboratories – Ultra Low Power, 8-2 kB Flash, Capacitive Sensing MCU

C8051F99x-C8051F98x
18. Reset Sources
Reset circuitry allows the controller to be easily placed in a predefined default condition. On entry to this
reset state, the following occur:
 CIP-51 halts program execution
 Special Function Registers (SFRs) are initialized to their defined reset values
 External Port pins are forced to a known state
 Interrupts and timers are disabled
All SFRs are reset to the predefined values noted in the SFR descriptions. The contents of RAM are
unaffected during a reset; any previously stored data is preserved as long as power is not lost. Since the
stack pointer SFR is reset, the stack is effectively lost, even though the data on the stack is not altered.
The Port I/O latches are reset to 0xFF (all logic ones) in open-drain mode. Weak pullups are enabled
during and after the reset. For power-on resets, the RST pin is high-impedance with the weak pull-up off
until the device exits the reset state. For V_DD Monitor resets, the RST pin is driven low until the device exits
the reset state.
On exit from the reset state, the program counter (PC) is reset, and the system clock defaults to an internal
oscillator. Refer to Section “19. Clocking Sources” on page 188 for information on selecting and
configuring the system clock source. The Watchdog Timer is enabled with the system clock divided by 12
as its clock source (Section “26.4. Watchdog Timer Mode” on page 311 details the use of the Watchdog
Timer). Program execution begins at location 0x0000.
Important Note: On device reset or upon waking up from Sleep mode, address 0x0000 of external
memory may be overwritten by an indeterminate value. The indeterminate value is 0x00 in most situations.
A dummy variable should be placed at address 0x0000 in external memory to ensure that the application
firmware does not store any data that needs to be retained during sleep or reset at this memory location.
Px.x
Px.x
Comparator 0
+
-
C0RSEF
VDD
VDD
Supply
Monitor
+
-
Enable
Power On
Reset
(wired-OR)
'0'
RST
SmaRTClock
RTC0RE
Missing
Clock
Detector
(one-
shot)
EN
PCA
WDT
EN
Reset
Funnel
(Software Reset)
SWRSF
Illegal Flash
Operation
System
Clock
CIP-51
Microcontroller
Core
System Reset
Extended Interrupt
Handler
Power Management
Block (PMU0)
Reset
System Reset
Power-On Reset
Figure 18.1. Reset Sources
Rev. 1.2
181