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Draw internal RAM organisation of 89C51 microcontroller. Explain register banks in it.
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  • The 89c51 has 128 byte internal RAM and divided into 3 parts/area.

In first part :

  • 32 bytes from addresses 00H to 1FH i.e. 32 registers organised in 4 banks. Each bank contains 8 registers (each of 8 bit) and available at each address.

  • Registers are named as:

Bank 0 –R0, R1, R2, R3, R4, R5, R6, R7

Bank 1 –R0, R1, R2, R3, R4, R5, R6, R7

Bank 2 –R0, R1, R2, R3, R4, R5, R6, R7

Bank 3 –R0, R1, R2, R3, R4, R5, R6, R7

  • If register banks are not selected, it can be used as general purpose area.

  • On reset Bank 0 is selected.

  • RS1 and RS0 bits (D3 and D4) of PSW register are used to select the register bank.

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