C8051T630 Datasheet, PDF (95/221 Pages) Silicon Laboratories – Mixed-Signal Byte-Programmable EPROM MCU

C8051T630/1/2/3/4/5
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 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 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. The Watchdog Timer is enabled with the system clock divided by 12 as its clock source. Pro-
gram execution begins at location 0x0000.
Px.x
Px.x
EXTCLK
Low
Frequency
Oscillator
Internal
Oscillator
External
Oscillator
Drive
Comparator 0
+
-
C0RSEF
VDD
Supply
Monitor
+
-
Enable
Power On
Reset
'0'
(wired-OR)
Missing
Clock
Detector
(one-
shot)
EN
PCA
WDT
EN
Reset
Funnel
(Software Reset)
SWRSF
Illegal
EPROM
Operation
System
Clock
Clock Select
CIP-51
Microcontroller ^{System Reset}
Core
Extended Interrupt
Handler
Figure 18.1. Reset Sources
/RST
Rev. 1.0
95