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Radiant 11Sep2007 12:35

Temp Reg Instruction
Microprocessor: 8085

I know that W and Z are the temporary registers

They are not available to the users.

And they are used only by the microprocessor for the internal operations.

But which are the instructions that microprocessor uses to perform the operations?

I never came across any instruction (out of the 74 instructions) that supports the temporary registers.

DaWei 11Sep2007 13:43

Re: Temp Reg Instruction
Internal operations of the processor are governed by microcode and hardware logic signals instituted by the chip designer. You cannot affect these.

Radiant 11Sep2007 13:51

Re: Temp Reg Instruction
So does it mean that there is no one instruction where these registers are used by microprocessor?

DaWei 11Sep2007 14:56

Re: Temp Reg Instruction
These registers are not used by the programmer. Data is moved around inside the chip by switching logic elements in a way consistent with carrying out an instruction. An example would be in connecting the various general purpose registers to the ALU.

Do not forget that a microprocessor is a hardware device. Software is merely a list of easily-modifiable instructions that control the signals applied to the hardware elements. A single software instruction is merely a pattern of bits that cause certain signals to be applied in an appropriate sequence.

Perhaps you should resort to Google for information on microprocessor architectures.

Radiant 11Sep2007 15:59

Re: Temp Reg Instruction
I just now read that CALL instruction makes use of the W and Z registers for storing the next address just after the "CALL addr " instruction; that is the address to which it has to return after it completes executing the Subroutine!

Thank you very much !

DaWei 12Sep2007 02:49

Re: Temp Reg Instruction
That's just a temporary storage, though. It's then pushed onto the stack so that nested calls (and interrupts) will work.

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