C8051F340/1/2/3/4/5/6/7

11. 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 pull-ups 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. Refer to Section “14. Oscillators” on page 135 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 “22.3. Watchdog Timer Mode” on page 272 details the use of the Watchdog Timer). Program execution begins at location 0x0000.

VDD

Px.x

Px.x

 

 

 

 

Internal LF

 

 

 

 

 

Oscillator

 

 

 

 

 

 

 

 

 

 

 

 

Internal HF

 

 

 

 

 

Oscillator

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Clock

 

 

 

 

 

Multiplier

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

External

 

XTAL1

 

Oscillator

 

XTAL2

 

 

 

 

Drive

 

 

 

Supply

Monitor

+Enable

-

 

 

 

 

 

 

 

 

Power On

 

 

 

 

 

Comparator 0

Reset

'0'

 

 

/RST

 

 

 

 

 

(wired-OR)

 

 

 

 

+

 

 

 

-

C0RSEF

 

 

 

 

 

Missing

 

 

 

Clock

 

 

Reset

Detector

 

 

(one-

PCA

 

Funnel

shot)

Software Reset (SWRSF)

 

EN

WDT

 

 

 

 

 

 

 

 

Errant

 

 

EN

FLASH

Enable

MCD Enable

WDT Enable

Operation

 

System

 

USB

VBUS

Clock

CIP-51

 

Controller

Transition

Microcontroller

System Reset

 

 

Core

 

 

Clock Select

Extended Interrupt

Handler

Figure 11.1. Reset Sources

Rev. 0.5

101

Page 101
Image 101
Silicon Laboratories C8051F344, C8051F347, C8051F346, C8051F341, C8051F343, C8051F340, C8051F345, C8051F342 Reset Sources