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2 votes

Is there any way to read current Interrupt Mode in Z80 machine code?

Is there any way to read current Interrupt Mode in Z80 machine code? By the CPU alone: No. Also, why should it? Interrupt mode chosen is related to the hardware of a system, nothing that would make ...
Raffzahn's user avatar
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5 votes
Accepted

Is there any way to read current Interrupt Mode in Z80 machine code?

The Mirage Microdriver (a snapshot device for the ZX Spectrum) needs to record the current interrupt mode when a snapshot is made. It does this by setting I to 80h and storing the address of an ...
john_e's user avatar
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1 vote

Could the Z80 do interference-free video as the 6502 could?

To add to the Spectrum answer: the transparent video access was used in Spectrum 128, not just the clones. Not that it matters. Indeed the method used required memory access time of 1 clock cycle. But ...
AlexFreed's user avatar
3 votes

Does Altair Basic actually risk wiping itself out of memory in its auto-memsize initialization?

Given an all RAM 64k system, doesn't this loop effectively wipe itself out of memory? Seems quite like it. As well visible here. The question: Was the design of the Altair such that it was ...
Raffzahn's user avatar
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0 votes

Could the Z80 do interference-free video as the 6502 could?

The Amstrad CPC range of Z80 machines 'solved' this problem by interleaving RAM reads by the video gate array with Z80 read and writes. As some Z80 M-states last 3 clock cycles, and some last 4 clock ...
Mark Williams's user avatar
9 votes

Why is Z80 called a 8-bit CPU?

No one seems to have (as yet) mentioned that the ALU was only 4-bit, which muddies the waters even further - so I'll throw that into the ring as well. So, the Z80 had: 4 bit ALU; 8 bit data bus, and;...
Greenonline's user avatar
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13 votes
Accepted

Why is Z80 called a 8-bit CPU?

CPUs are about Data Why is Z80 called a 8-bit CPU? A CPU's 'size' is about the main data type it processes, not secondary types or how much thereof it can access. The Z80 fetches, processes and ...
Raffzahn's user avatar
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7 votes

Why is Z80 called a 8-bit CPU?

It works on 8-bit numbers. It has 8-bit data bus, both externally and internally. There is no operation that can be performed in a single 16-bit operation, and the specific example of adding two 16-...
Justme's user avatar
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7 votes

Why is Z80 called a 8-bit CPU?

There is no well-defined test for the ‘bitness’ of a CPU; it’s marketing as much as anything else. The Z80 was considered an 8-bit CPU in its day because it has an 8-bit data bus and an overwhelming ...
Tommy's user avatar
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