I'm a little confused over the concept of machine code... Is machine code synonymous to assembly language? What would be an example of the machine code in LC-3?
+3
A:
An "Assembly language" is a symbolic (human-readable) language, which a program known as the "assembler" translates into the binary form, "machine code", which the CPU can load and execute. In LC-3, each instruction in machine code is a 16-bit word, while the corresponding instruction in the assembly language is a line of human-readable text (other architectures may have longer or shorter machine-code instructions, but the general concept it the same).
Alex Martelli
2009-12-25 20:10:46
thank you, alex!a few examples of LC-3 instructions are ADD, LDI, LDR, and this would be assembly language1001010111010111 <== machine code but what is a 16-bit word? ADD, LDI, LDR? how are they 16 bit?
2009-12-25 20:27:39
1001010111010111 are exactly 16 bits -- so, that's an example of machine code, and of a 16-bit word. Symbolic notation such as `ADD` and `LDI` (each of which is a string of 3 ASCII characters) is part of the assembly language, i.e. the textual notation which the assembler program can translate to binary machine code (words of 16 bits each, in the case of LC-3 in particular).
Alex Martelli
2009-12-25 20:33:42
now im looking at the following image, what in the world is this?http://www.rev101.com/pics/010editor.jpg
2009-12-25 20:36:45
A:
The above stands true for any high level language (such as C, Pascal, or Basic). The differece between HLL and assembly is that each assembly language statement corresponds to one machine operation (macros excepted). Meanwhile, in a HLL, a single statement can compile into a whole lot of machine code.
You can say that assembly is a thin layer of mnemonics on top of machine code.
Seva Alekseyev
2009-12-25 20:22:33
+4
A:
Assembly instructions (LD, ST, ADD, etc. in the case of the LC-3 simulator) correspond to binary instructions that are loaded and executed as a program. In the case of the LC-3, these "opcodes" are assembled into 16-bit strings of 1s and 0s that the LC-3 architecture is designed to execute accordingly.
For example, the assembly "ADD R4 R4 #10" corresponds to the LC-3 "machine code":
0001100100101010
Which can be broken down as:
0001 - ADD. 100 - 4 in binary 100 - 4 in binary 10 - indicates that we are adding a value to a register 1010 - 10 in binary
Note that each opcode has a distinct binary equivalent, so there are 2^4=16 possible opcodes.
The LC-3 sneakily deals with this problem by introducing those flag bits in certain instructions. For ADD, those two bits change depending on what we're adding. For example, if we are adding two registers (ie. "ADD R4 R4 R7" as opposed to a register and a value) the bits would be set to 01 instead of 10.
This machine code instructs the LC-3 to add decimal 10 to the value in register 4, and store the result in register 4.
ty
2009-12-25 20:28:46
thank you typpo, this is very informative. But will you explain why is 10 1001 in binary.( I thought it was 1010) and 4 is 0100 in binary (in the example, 4 has two different binary values 0010 and 1010)...
2009-12-25 20:34:38
My mistake - I wrote out the numbers quickly and wasn't thinking. You are correct of course. Sorry for the confusion.
ty
2009-12-25 20:39:20
thank you typpo, can you breifly explain if the following image is of relevance to what we just discussed? Thanks http://www.rev101.com/pics/010editor.jpgim guessing the 0000h would be memory locations? but everything else, i don't know...
2009-12-25 20:46:41
Hex editors display the hexadecimal equivalent of binary instructions, for example our instruction '0001100100101010' above has a hexadecimal equivalent of '192A'. If applicable, your hex editor also shows an ASCII equivalent.
ty
2009-12-25 20:58:44