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Rom

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http://alltypeim.blogspot.in/

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Rom

  1. 1. INTRODUCTION OF ROM – Read Only Memory http://alltypeim.blogspot.in/
  2. 2. ROM  Concept  Characteristics of the ROM BIOS  ROM Types  ROM Internal Structure  ROM Implementation  ROM Implementation of a Moore Machine  ROM Implementation of a Mealy Machine  ROM Array Layout  Row Decoders  Complete ROM Layout  Summary http://alltypeim.blogspot.in/
  3. 3. Concept Is read-only memory. Do not lose data when power is lost. ROM memory is used to produce chips with integrated CMOS BIOS program http://alltypeim.blogspot.in/
  4. 4. Characteristics of the ROM BIOS BIOS ROM containing the software configuration and system diagnostics, and routine input / output low level that DOS uses. These programs are encoded in ROM and is called firmware. An important feature of the ROM BIOS is detecting new hardware in the computer and reconfigure the operating system as device driver. http://alltypeim.blogspot.in/
  5. 5. ROM Types  PROM (Programmable Read Only Memory):  Type of ROM that information is only installed once.  The CD can be called PROM.  EPROM (Erasable Programmable ROM):  Type of ROM that can erase and rewrite it.  "CD-Erasable" can be called EPROM.  EEPROM (Electronic Erasable Programmable ROM):  It form enhence of EPROM, a difference compared to the EPROM is able to write and remove the information again and again by software rather than hardware.  Example: "CD-Rewritable".  Application specific EEPROM is "flash BIOS". ROM is the type of information can install or upgrade software. http://alltypeim.blogspot.in/
  6. 6. ROM Internal Structure ... n Inputs Lines n bit decoder ... m Outputs Lines . . . Memory Array 2n words x m bits http://alltypeim.blogspot.in/
  7. 7. ROM Implementation • 16-word x 5 bit ROM ROM L, R S1:0 TL, TR, F S'1:0 S1 ' S0 ' TR'TL' F' 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 4:16DEC S1 S0 L R http://alltypeim.blogspot.in/
  8. 8. ROM Implementation • 16-word x 5 bit ROM ROM L, R S1:0 TL, TR, F S'1:0 S1 ' S0 ' TR'TL' F' 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 4:16DEC S1 S0 L R http://alltypeim.blogspot.in/
  9. 9. ROM Implementation of a Moore Machine  ROMs implement combinational logic  Note that ROMs do not hold state  How would you determine the maximum clock frequency of this circuit? Look at the FF to FF path (NS to PS) ROM ROM Present State Next State Outputs Inputs http://alltypeim.blogspot.in/
  10. 10. ROM Implementation of a Mealy Machine  ROMs implement combinational logic  Note that ROMs do not hold state  How would you determine the maximum clock frequency of this circuit?  Look at the FF to FF path (NS to PS) ROM ROMPresent State Next State Outputs Inputs http://alltypeim.blogspot.in/
  11. 11. ROM Array Layout Unit cell is 12 x 8 l (about 1/10 size of SRAM) Unit Cell http://alltypeim.blogspot.in/
  12. 12. Row Decoders ROM row decoders must pitch-match with ROM Only a single track per word! http://alltypeim.blogspot.in/
  13. 13. Complete ROM Layout http://alltypeim.blogspot.in/
  14. 14. Summary  ROMs provide stable storage for data  ROMs have address inputs and data outputs ROMs directly implement truth tables  ROMs can be used effectively in Mealy and Moore machines to implement combinational logic  In normal use ROMs are read-only They are only read, not written  ROMs are often used by computers to store critical information Unlike SRAM, they maintain their storage after the power is turned off http://alltypeim.blogspot.in/

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