Is anyone interested with the Z80?

The 6502 was used in the schools BBC Micro but strangely enough we never

looked at the individual transistors when I was at school.

We did at uni but not that processor.

I've used both of these micros and you're trying to compare apples and lychees.

Each micro has its own strengths and weaknesses.

The most important thing is whether you can accomplish your desired task quickly and easily.

VHDL, Verilog and programming models don't necessarily tell you the real story about what's inside the ICs!

To do that you have to look at the actual die designs.

These processors were aimed at different markets.

The Z80 was specifically designed to be backward compatible with the Intel 8080 so that it could immediately run a vast amount of software. About 60% of its die is dedicated for instruction decoding. It also has built in DRAM refresh support.

The 6502 used a different approach. It is a cheap clone of the 6800 and due to its lower price was used by many manufacturers.

The Apple ][ needed a plug in Z80 board to access the loads of Z80 CP/m software.

One obvious reason why the Z80 uses more transistors than a 6502 is because it has four times as many registers than the 6502) and that means lots more transistors are needed.

As for speed, did you know the Z80 can exchange the contents of two 16 bit registers in 4 T states. That's 1uS @ 4MHz.

Later versions of the Z80 can run up to 50MHz with single cycle execution - That's 20ns for the 16 bit register exchange instruction. Try that with a 6502!

(If a 4GHz version were built it'd be 250ps!)

As for stack size and flexibility the Z80 can have its stack located at any memory location and be of any size. The 6502 has a fixed size of 256 bytes at a fixed address.

As for provability NASA must of thought it cut the mustard because the Z80 was used on the Space Shuttle.

I'll raise your 50MHz ........

https://en.wikipedia.org/wiki/WDC_65C02

re provability  - I told you no one cared - the VIPER was a total flop (and that's about how fast it was )

It's interesting that when people have built fast versions of old architectures it hasn't turned out to be good business - remember Scenix and the 100MHz PIC ?

MK

Programmable logic doesn't count because it can be applied to both!

Programmable logic excels at counting

Have a nice day !

MK

More on the Z80 vs 6502 debate

1. The Z80 can run quite complex programs without any external RAM because of its relatively large number of internal registers unlike the 6502 which has just a few registers and is reliant on page $0 (00-FF) memory to provide full functionality.

This fact is great for Z80 test and servicing programs where faulty RAM can be easily detected.

2. Comparisons of their clock rates are irrelevant because they both operate from different timing schemes.

The 6502 timing scheme makes it easy to accomplish shared memory access without any contention (but requires double speed memory to do so).

Yes, but what to do? Run CPM.

If you just want to run CP/m then build my mbed virtual machine. It supports video output, USB peripherals with SDCards!

Ladder is a great game to play with it.

For its time, I found that the Z80 was an excellent tuition tool.

To get the best results one had to design and build their own hardware and not just use it.

That fun doesn't occur with premade SMT microcontrollers.

One had to experience the aha moments and fails along the way.

Did you know that the Texas Instruments TI-83 and Ti-84 calculators have Z80s in them?

In fact you can program them in Z80 assembly language.

There's also one with a 68000!

Did you know the Intel 4004 processor and chipset of a total four chips were designed for the Busicom 141-PF printing calculator. The Story of the Intel 4004 to read more.

Clem