Microprocessor having low power internal oscillator capabilities

Abstract

An 8051 microprocessor core having an ability to operate via an external crystal oscillator or be switched to operate in a low power mode via an internal ring oscillator.

What is claimed is:  
     
         1 . A microprocessor, comprising: 
 a four cycle 8051 microprocessor core;    a crystal oscillator circuit for providing timing signals to said four cycle 8051 microprocessor core;    a means for connecting an external crystal oscillator to said crystal oscillator circuit;    a switching circuit, connected to said an output of said crystal oscillator circuit, for providing a timing output to said microprocessor; and    a ring oscillator circuit, for providing timing signals to said four cycle 8051 microprocessor core, connected to said switching circuit, said switching circuit being for switching between said crystal oscillator and said ring oscillator to provide said timing output.    
     
     
         2 . The microprocessor of    claim 1   , wherein when said switching circuit is switched to said ring oscillator then said microprocessor is in a low power state.  
     
     
         3 . The microprocessor of    claim 1   , wherein said output of said switching circuit is input into a divide-by circuit, said divide-by circuit being controllable to divide said timing output from said switching circuit by a plurality of divisors.  
     
     
         4 . The microprocessor of    claim 3   , wherein said divide-by circuit is software controllable.  
     
     
         5 . A microcontroller, comprising: 
 a microcontroller core circuitry utilizing at least a portion of standardized 8051 instruction set;    an internal ring oscillator for producing a first oscillation signal;    a means for connecting to an external crystal oscillator;    crystal oscillation circuitry for producing a second oscillation signal, said crystal oscillation circuitry adapted to connect to said means for connecting and external crystal oscillator;    a switching circuit, receiving said first oscillation signal and said second oscillation signal, for switching between said first oscillation signal and said second oscillation signal, said switching circuit providing an output,    a plurality of divide-by circuits, receiving said output from said switching circuit, each said divide-by circuit providing a divided output;    means for selecting one of said divided outputs and for providing said selected divided output as a timing signal to said microcontroller core circuitry.    
     
     
         6 . The microcontroller of    claim 5   , wherein when said switching circuit is switched to said ring oscillator said microcontroller is operating in a power management mode.  
     
     
         7 . The microcontroller of    claim 5   , wherein said microcontroller core is a 4 cycle high speed microcontroller core.  
     
     
         8 . The microcontroller of    claim 5   , further comprising software control adapted to switch said switching circuit between said internal ring oscillator and said crystal oscillation circuitry.  
     
     
         9 . The microcontroller of    claim 5   , comprising a power management mode which requires said microcontroller to operate at lower clock speeds and use less energy.  
     
     
         10 . The microcontroller of    claim 5   , further comprising software control to turn off said crystal oscillation circuitry and operate said microcontroller core circuitry using said internal ring oscillator.  
     
     
         11 . The microcontroller of    claim 5   , wherein said microcontroller core circuitry is an 8-bit microcontroller core circuit.  
     
     
         12 . An integrated circuit comprising: 
 a microcontroller circuit core;    an internal oscillator circuit that can provide a first timing signal to said microcontroller core;    an external crystal oscillator connection for receiving a second timing signal that can be provided to said microcontroller circuit;    a switching means, under software control, for switching between said first timing signal and said second timing signal and providing one of said first timing signal and said second timing signal to said microcontroller core.    
     
     
         13 . The integrated circuit of    claim 12   , further comprising a means for dividing timing signals down and for providing said divided down timing signal to said microcontroller core, said means for dividing down said timing signal providing a plurality of discrete divided down timing signals.  
     
     
         14 . The integrated circuit of    claim 12   , wherein said microcontroller circuit core can operate using at least standard 8051 microprocessor instructions.  
     
     
         15 . The integrated circuit of    claim 12   , wherein said microcontroller circuit core is a 4-cycle 8051 style microcontroller core.  
     
     
         16 . The integrated circuit of    claim 12   , wherein said internal oscillator circuit is a ring oscillator circuit.