The Z80 Registers
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The Essence of Registers
Again, much simpler than you could possibly imagine !!
Picture a wall containing a number of pigeon-holes…
Registers are exactly the same but can only contain a number - an integer, positive value
So, in Image#1 below, Register A is an 8-bit register so it can only ever contain an 8-bit number between 0000 0000 to 1111 1111 (in binary) and the equivalent values in hexadecimal are 00 to FF and in decimal, 0 to 255
And that is it !
The real cleverness comes in when those simple numbers are used to represent something with meaning within a particular context… 1
One very basic & fundamental context is that of the computer’s Instruction Set 2
Another context is that of representing alphabetic letters as numbers, known as “ASCII” and Extended ASCII and further extended as in the Unicode system More about this
The Z80 Registers
The Z80 Registers 3 - Image#1 (Husband, 2022)
Register A - The Accumulator
The BC, DE & HL Register Pairs
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And this is entirely the responsibility of the programmer. Remember what Petzold said: “The Annotated Turing” (Wiley 2008), Page 127, “In this digital age of ours we have grown used to representing all forms of information as numbers. Text, drawings, photographs, sound, music, movies – everything goes into the digitisation mill and gets stored on our computers and other devices in ever more complex arrangements of 0s and 1s…” That is a very large number of different contexts ! ↩
The microprocessor MUST ALWAYS be running instructions - See: real-code, and in doing that it has a very powerful ability to process data ↩
These are not all of them - the image is a abstraction… There is another identical set of registers called the “alternate register set” ↩