8.12

Used to Hold fixed code (ex. BIOS), tables of data (ex. FSM next state/output logic), slowly changing values (date/time on computer)

Mask ROM -

• Used with logic circuits for tables etc.
• Contents fixed at IC fab time (truly write once!)

EPROM (erasable programmable) & FLASH

• requires special IC process (floating gate technology)

  
  

  
  

  
  

  
  

  
  

  
  

  
  

• writing is slower than RAM. EPROM uses special programming system to provide special voltages and timing.
• reading can be made fairly fast.
• rewriting is very slow.
  • erasure is first required
  • EPROM - UV light exposure

    
    

    
    

    
    

    
    

    
    

    
    (because of extra cost of special package, most parts are shipped without erasure option.)

Data sheet for AM27x040