C8051F50x-F51x
17. 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 dur-
ing and after the reset. For VDD 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. The Watchdog Timer is enabled with the system clock divided by 12 as its clock source. Pro-
gram execution begins at location 0x0000.
VDD
Power On
Reset
Supply
Monitor
+
-
'0'
/RST
Enable
Comparator 0
(wired-OR)
Px.x
Px.x
+
-
C0RSEF
Missing
Clock
Detector
(one-
shot)
Reset
Funnel
PCA
WDT
(Software Reset)
EN
SWRSF
EN
Errant
FLASH
Operation
System
Clock
CIP-51
System Reset
Microcontroller
Core
Extended Interrupt
Handler
Figure 17.1. Reset Sources
Rev. 1.1
141
SILICON [ SILICON ]
