All Questions
Tagged with instruction-set z80
6
questions
13
votes
1
answer
593
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Ratio of code density between 8080 and Z80
The Z80 was (except for a handful of tiny incompatibilities) a superset of the 8080, adding a number of new instructions as well as the alternate register set. It seems therefore that it must have at ...
- 63.1k
16
votes
1
answer
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Why does the Z80 not have EX DE, IX?
Reading Decoding Z80 Opcodes, There's a section about the 0xDD prefix. This instruction prefix causes the next instruction to use the IX register instead of the HL register. That makes sense. HL and ...
- 39.3k
16
votes
1
answer
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What are the "ports" used via IN/OUT, vs. the PEEK/POKE address space?
This is something of a followup to How much control of TRS-80 Model III disk drives was possible from its Cassette (ROM) BASIC? but on a more general topic:
I know that PEEK and POKE enable direct ...
- 2,947
32
votes
6
answers
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Why does the Z80 include the RLD and RRD instructions?
The Z80 has an instruction RLD, which apparently treats the lower 4 bits in the accumulator and the full 8 bits in (HL) as a twelve bit integer which it then rotates left by 4 bits. The carry flag ...
- 39.3k
33
votes
2
answers
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What is the relative code density of 8-bit microprocessors?
When RAM is at a premium, as it was in the old days, a greater code density of an instruction set can be a substantial advantage.
(Click saver: Code density refers loosely to how many microprocessor ...
- 19.4k
50
votes
2
answers
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How did the Z80 instruction set differ from the 8080?
The Zilog Z80 microprocessor, known for its use in the ZX Spectrum, was designed to be a backwards-compatible extension to the Intel 8080 processor. It introduced several new instructions to the 8080'...
- 18.7k