New answers tagged

1

Forgive me if this is a repeat, but I didn’t see it mentioned. If 8080 compatibility isn’t needed, the ability to swap an entire register set instead of using a stack makes context switching faster, especially for an interrupt service routine.


1

I'm not familiar with the 8080's internal design, but the Z80 had, in addition to a general-purpose four-bit ALU, a separate 16-bit limited-function ALU (operations limited to adding or subtracting one) which sat on a 16-bit bus with all of the registers. In addition, a few of the 16-bit registers like PC and SP were isolated from the rest of the registers ...


12

Possibly a simple logic trick. The slow path in addition is carry propagation (not the individual half-adders). You can thus often double the clock rate by pipelining the carry. If you pipeline the carry, then you can reuse the bit adders at the beginning of the chain, and put them at the end. Depending on the ratio between pipeline registers, reuse ...


11

Why did the Z80 with 4-bit ALU out-perform the fully 8-bit Intel 8080? Did it? I guess this depends on what 'performance' meant here. If it's about instructions per clock, then No. They are, for all practical purposes, identical. If it's about reaching higher clock speed, then Yes. If it's about an increased instruction set, then as well Yes. If it's about ...


23

... a scaled-down, cost-reduced, clone of the Intel 8080. The Z80 had a massively extended instruction set, featured more addressing modes and had more registers than the 8080. It also had a built-in DRAM refreshing logic. ... and it was more expensive than the 8080! This is the opposite of "cost-reduced". It only used a 4-bit ALU. I assume this would ...


0

Making your own Z80 computer is the subject of several books written in the 80s, such as Byte Books' Build Your Own Z80 Computer: Design Guidelines and Application Notes by Steve Ciarcia, which is freely available online and Beginners Guide to Computers & Microprocessors with projects by Adams. You've correctly anticipated that the computers that these ...


2

Are you interested in running any particular kind of older software, once you've gotten it working? That should dictate what kind of CPU you use. For example, if running WordStar or Zork is paramount you'd want to use a Z80. All the processors have their special fun features. Don't discount the 6809, either. To answer the question, yes it is possible. ...


Top 50 recent answers are included