C8051F300/1/2/3/4/5
Rev. 2.9
83
9.
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 detailed descriptions. The contents of internal
data memory are unaffected during a reset; any previously stored data is preserved. However, 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 V
DD
Monitor and power-on 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 the inter-
nal oscillator. Refer to
Section “11. Oscillators” on page 97
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 “16.3. Watchdog Timer Mode” on page 164
details the use of the Watchdog Timer).
Once the system clock source is stable, program execution begins at location 0x0000.
Figure 9.1. Reset Sources
PCA
WDT
Missing
Clock
Detector
(one-
shot)
(Software Reset)
System Reset
Reset
Funnel
P0.x
P0.y
EN
SWRSF
Internal
Oscillator
System
Clock
CIP-51
Microcontroller
Core
Extended Interrupt
Handler
Clock Select
EN
WDT
Enable
MCD
Enable
XTAL1
XTAL2
External
Oscillator
Drive
Illegal
FLASH
Operation
+
-
Comparator 0
C0RSEF
/RST
(wired-OR)
Power On
Reset
+
-
VDD
Supply
Monitor
Enable
'0'
Summary of Contents for C8051F300
Page 2: ...C8051F300 1 2 3 4 5 2 Rev 2 9 NOTES ...
Page 6: ...C8051F300 1 2 3 4 5 6 Rev 2 9 NOTES ...
Page 48: ...C8051F300 1 2 3 4 5 48 Rev 2 9 NOTES ...
Page 56: ...C8051F300 1 2 3 4 5 56 Rev 2 9 NOTES ...
Page 82: ...C8051F300 1 2 3 4 5 82 Rev 2 9 NOTES ...
Page 88: ...C8051F300 1 2 3 4 5 88 Rev 2 9 NOTES ...
Page 96: ...C8051F300 1 2 3 4 5 96 Rev 2 9 NOTES ...
Page 130: ...C8051F300 1 2 3 4 5 130 Rev 2 9 NOTES ...
Page 172: ...C8051F300 1 2 3 4 5 172 Rev 2 9 NOTES ...