GENERAL PURPOSE RAM FOR MICROCONTROLLER

• M/c uses separate spaces for data and code.
• Internal memory of m/c consists of on chip code memory and data memory which is “RAM”.
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• On chip RAM consist of general purpose registers, bit addressable locations and special purpose registers.
• General purpose RAM starts from 30 H and ends at 7FH.
• Any location of RAM can be addressed freely using direct or indirect addressing modes.
• For example to read the contents of location 5FH into accumulator we use instruction

                       MOV A, 5FH

• This is direct addressing and instruction will copy all the contents of location 5FH into accumulator.
• RAM can also be assessed by indirect addressing mode for example

 

              MOV R0, #5FH

             MOV A,@R0

• First instruction is immediate addressing and will load value 5FH in register R0.
• Second instruction represents indirect addressing mode and will copy data contents pointes by register R0.