68000 Registers

General Purpose Registers

1. D0 - D7 (Data Registers)

   • Used for arithmetic, logic operations, and data storage.

   • Example:

     MOVE.L #10, D0 ; Move immediate value 10 into D0 ADD.L #5, D0 ; Add 5 to D0, result in D0

2. A0 - A7 (Address Registers)

   • Used for addressing memory locations.

   • Example:

     LEA $1000, A0 ; Load effective address $1000 into A0 MOVE.L (A0), D1 ; Move the value at address in A0 into D1

Stack Pointer

1. A7 (User Stack Pointer, USP)

   • Points to the top of the user stack.

   • Example:

     MOVE.L A7, USP ; Move the value of A7 to USP

2. SSP (Supervisor Stack Pointer)

   • Points to the top of the supervisor stack.

   • Example:

     MOVE.L A7, SSP ; Move the value of A7 to SSP

Program Counter

1. PC (Program Counter)

   • Points to the next instruction to be executed.

   • Example:

     JMP $3000 ; Jump to address $3000, PC is updated to $3000

Status Register

1. SR (Status Register)

   • Contains condition codes and control bits.

   • Example:

     ANDI #$F8FF, SR ; Clear interrupt priority bits in SR

Condition Code Register

1. CCR (Condition Code Register)

   • Contains condition flags (Negative, Zero, Carry, Overflow, Extend).

   • Example:

     ADDI.B #1, D0 ; Add 1 to D0, update condition flags in CCR

These registers are essential for various operations in 68000 assembly programming, providing the necessary functionality for arithmetic, data manipulation, control flow, and memory access.