How is an Assembly Language Processed by a CPU's Circuitry?

I'd like to have a bit more understanding of how, on a circuitry/hardware level, an assembler program works.

I think I have a very broad-brush understanding of how a CPU would process machine code on a hardware level. Please bear with me for this very generalised, hypothetical example:

If you took 00101110 in machine code, with the first part 0010 as an opcode and the second part 1110 as location address...

I think I understand, broadly, how those 8 bits of data would be fed along 8 wires to an instruction register, and how from there, the opcode 0010 gets fed along 4 wires into a variety of checking circuits to check the opcode, and a checking circuit would output true if if the opcode corresponded to the configuration of that circuit. Like this (yes I've been watching crash course computer science):

And i think I understand how, in broad terms, the location address 0111 would be sent along 4 wires that feed into multiplexors attached to four latch matrices, causing address location 0111 to be accessed in each of those matrices, each of which then feeds back whether its data bit at the location was a 1 or 0 / on or off.

What I'm saying is that I think I can begin to see, or at least imagine, how a processor 'processes' a binary number, on the level of hardware/circuitry, without it seeming like magic.

My question is, can someone explain to me on this level how a CPU, as part of an assembler, would translate assembly code?

For example, how would the circuitry take MOV EAX [EBX] and act on that as an instruction? I know that it would parse it, etc., but HOW does it parse it, on the level of wiring? Like how does it take a 'MOV' and translate that into the correct configuration of on/off wires?

On a related note, obviously the 'MOV' isn't stored as 'MOV' in the computer's memory - it's stored in binary. So if it's already stored in binary, why do we need to bother to translate it to a different binary configuration using an assembler?

An assembler is a program that reads assembly language commands and translates then into a sequence of binary instructions, addresses and data values that is called machine code. The machine code is stored in the computer's memory and can be executed by the computer at some later time. Machine code is read and "understood" directly by the CPU.

So a command such as "load the value 10 into register A" might be written in assembly language as "LDA 10" and then stored in machine code as one byte 00101010. The first four bits of the machine code instruction 0010 represent the LDA instruction and the second four bits 1010 represent the value that is to be loaded.

Note that the assembler makes life easier for the programmer by translating the "LDA" instruction and translating the value 10 from decimal to binary. It will also do other stuff like allowing the programmer to use labels, which it then translates into specific memory addresses.

In the simplest CPU architecture, when the CPU executes the instruction 00101010 it actually runs a sequence of low level microinstructions which will be something like this:

• Add 1 to the register that tells the CPU where the next instruction is stored in memory

• Set a control line to take control of the data bus.

• Load the lowest four bits of the machine code instruction onto the data bus.

• Release control of the data bus.

• Set a control line to tell Register A to read and store the value on the data bus.

• Read the next instruction from memory.

In the very simplest/oldest CPU architecture this final translation from machine code to microinstructions is hard wired in logic gates.

A good guide to this sort of stuff for beginners is "But How Do It Know".

Bonus question: If an assembler is a program that creates other executable programs, how is the assembler created in the first place ?

StackExchange Computer Science Q#110241, answer score: 4