Tanenbaum and MSX

By iamweasel2

Hero (604)

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10-10-2020, 16:28

I'm reading Tanenbaum's Structured Computer Organization and trying to map the things he says to MSX.

He explains at chapter two that some CISC machines have an interpreter, whose function is to break the instructions of its target machine into small steps. Those instructions are carried by the interpreter, which will break then in smaller instructions, which will execute in the actual hardware.

I was wondering, does Z80 has an interpreter inside that alllows him to have some complex instructions? If it does, what kind of instructions are interpreted on Z80?

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By albs_br

Master (146)

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10-10-2020, 18:07

For me it looks like some instructions (the ones that makes loops, such as LDIR) are executed on a higher level (not sure if interpreted is the right term)

By mcolom

Expert (112)

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10-10-2020, 18:08

Here there is an answer about that: https://retrocomputing.stackexchange.com/questions/6656/how-...
Z80 doesn't run microcode.

By iamweasel2

Hero (604)

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11-10-2020, 00:28

Thanks guys. Smile

By Sandy Brand

Master (196)

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11-10-2020, 01:42

After Z80 opcodes such as LDIR are completed, depending on the state of flags that are used for loop counting, the CPU will actually put the Program Counter back at the start address of LDIR opcode.

So the Z80 is literally repeatedly executing the same LDIR opcode (which includes fetching it from memory again, decoding, etc.) There is nothing 'smart' going on inside the CPU.