Question

Generate the equivalent Sim68 assembly program for the following machine code assuming it originates at address dollar 0000: 1001 0000 0100 0000 0011 0000 0100 0000 0011 0010 0010 1000 0000 0000 0000 1100 0110 0111 0000 0110 0110 1101 1111 1000 1101 0000 0100 0001 0110 0000 1111 0110 0100 1110 0100 0000 0000 0000 0000 0000 0001 0110 1111 0000 1111 1111 1111 1111 1000 0000 0000 0000 0000 0000 0000 0001

Answer 1

The given machine code starts at address $0000. The number of address bits in Sim68 is 24 bits. The number of data bits is 16 bits in Sim68 assembly language. The equivalent Sim68 assembly program for the given machine code is shown in the below table:

Address Machine code Sim68 instructions org $0000 sub do, do $0000 1001 0000 0100 0000 $0002 0011 0000 0100 0000 movea do, ao $0004 0011 0010 0010 1000 move 12 (а0), di $0006 0000 0000 0000 1100 (12) $0008 0110 0111 0000 0110 beq $0010 $000A 0110 1101 1111 1000 blt $0004 $000C 1101 0000 0100 0001 add di, do $000E 0110 0000 1111 0110 bra $0006 $0010 0100 1110 0100 0000 trap #0 $0012 0000 0000 0000 0000 dc $0000 $0014 0001 0110 1111 0000 dc $16F0 $0016 1111 1111 1111 1111 dc SFFFF $0018 1000 0000 0000 0000 dc $8000 $0020 0000 0000 0000 0001 dc $0001 end

Explanation: The instruction org defines the starting location of the program in the memory. The next machine code instruction is 1001 0000 0100 0000. The first 4 bits indicates the opcode of sub instruction. Then, the assembly code instruction is sub do, do. That mean, d0 = d0-do. Then, d0=0. The next machine code instruction is 0011 0000 0100 0000. The first 4 most significant bits indicates the opcode of movea instruction. The next 3 bits indicates destination address which do, the next 3 bits indicate destination mode, the next 3 bits indicate source mode, the next 3 bits indicate source address which is a. Then, the assembly code instruction is movea do, a0. The next machine code instruction is 0011 0010 0010 1000. The first 4 most significant bits indicates the opcode of move instruction. The next 3 bits indicate destination register address which is d1, the next 3 bits indicate addressing modes. The next 3 bits indicate the type of the addressing mode. Here, the addressing mode type value is 101 which is the address register indirect with displacement. Here, the displacement value is 12, the address register is al, and the destination address is dl. Then, the assembly code instruction is move 12 (а0), dl. The next machine code instruction is 0110 0111 0000 0110. The first 4 most significant bits indicates the opcode of beq instruction. The next 4 bits indicate condition. The remaining bits indicate the displacement value. Then, the assembly code instruction is beq $0010.

The next machine code instruction is 0110 1101 1111 1000. The first 4 most significant bits indicates the opcode of blt instruction. The next 4 bits indicate condition. The remaining bits indicate the displacement value. Then, the assembly code instruction is blt $0004. The next machine code instruction is 1101 0000 0100 0001. The first 4 most significant bits indicates the opcode of add instruction. The next 3 bits indicate destination address and the last 3 bits indicate source address. Then, the assembly code instruction is add di, do which means do = d0+d1 The next machine code instruction is 0110 0000 1111 0110. The first 4 most significant bits indicates the opcode of bra instruction. The last 8 bits indicate the displacement value. Then, the assembly code instruction is bra $0006. The next machine code instruction is 0100 1110 0100 0000. The first 4 most significant bits indicates the opcode of trap instruction which is used to stop. Then, the assembly code instruction is trap #0. The next 5 instructions define the constant values. The instruction end defines end of program.