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  # CPU 6502 

  The MOS Technology 6502 is an 8-bit microprocessor that was designed by a small team led by Chuck Peddle for MOS Technology.

  Popular home video game consoles and computers, such as the Atari 2600, Atari 8-bit family, Apple II, Nintendo Entertainment System, Commodore 64, Atari Lynx, BBC Micro and others, used the 6502 or variations of the basic design. 

  ### THE REGISTERS INSIDE THE 6502 MICROPROCESSOR

  Almost all calculations are done in the microprocessor. Registers are
  special pieces of memory in the processor which are used to carry out, and
  store information about calculations. The 6502 has the following registers:


  ### THE ACCUMULATOR

  This is THE most important register in the microprocessor. Various ma-
  chine language instructions allow you to copy the contents of a memory
  location into the accumulator, copy the contents of the accumulator into
  a memory location, modify the contents of the accumulator or some other
  register directly, without affecting any memory. And the accumulator is
  the only register that has instructions for performing math.


  ### THE X INDEX REGISTER

  This is a very important register. There are instructions for nearly
  all of the transformations you can make to the accumulator. But there are
  other instructions for things that only the X register can do. Various
  machine language instructions allow you to copy the contents of a memory
  location into the X register, copy the contents of the X register into a
  memory location, and modify the contents of the X, or some other register
  directly.


  ### THE Y INDEX REGISTER

  This is a very important register. There are instructions for nearly
  all of the transformations you can make to the accumulator, and the X
  register. But there are other instructions for things that only the Y
  register can do. Various machine language instructions allow you to copy
  the contents of a memory location into the Y register, copy the contents
  of the Y register into a memory location, and modify the contents of the
  Y, or some other register directly.
  
 

 ### Hello world - Load register
 
     ; This is a comment 
 
     LDX #3 
     ; load the X register 
     ; with value 3 (decimal)
     
     LDY #6
     ; load the Y register 
     ; with value 6 (decimal)
     
     LDA #7
     ; load the Accumulator
     ; with value 7 (decimal)
     
     LDX #$09
     ; load the X register 
     ; with value 9 (hexdecimal)
     
     LDY #$0a
     ; load the Y register 
     ; with value 0a (hexdecimal)
     ; 0a (hex) = 10 (decimal)
     
     LDA #$ff
     ; load the accumulator 
     ; with value ff (hexdecimal)
     ; ff (hex) = 255 (decimal)
     
     
     
 ### Storage
 
     LDX #$3 
     ; load the X register 
     ; with hex value 3 
     STX $010
     ; stores the value of the
     ; X register to memory location (010)

 ## Assembly on Sololearn 
 
 https://code.sololearn.com/c5D4FFxheYsW/?ref=app
     
 ### **References**
 - https://en.wikipedia.org/wiki/MOS_Technology_6502
 - http://skilldrick.github.io/easy6502/
 - http://nesdev.com/6502.txt
 

 
© Pedro H.J
6502_Tutorial
