I'm not at all sure one could fairly say the 6502 was a "stripped down M6800.
It has 56 documented instructions, not to mention the undocumented ones, so it's
probably not a RISC. The CMOS version has many more instructions, and it has
more addressing modes than the MOT processor.
It does store low-byte-first, though, so, in that respect, it's different from
the MOT parts.
Dick
----- Original Message -----
From: "Sipke de Wal" <sipke_at_wxs.nl>
To: <classiccmp_at_classiccmp.org>
Sent: Thursday, December 20, 2001 1:57 PM
Subject: Re: 6502/Z80 speed comparison (was MITS 2SIO serial chip?)
> The fact that the 6502 was a kinda striped-down version of
> the M6800, and was more efficient from a computing power
> perspective, has convinced some people that the 6502 was
> the first (and only 8-bit) RISC-processor.
>
> If the MOS people had given the chip more on board general
> purpose registers (i.e. like zero-page memory on-chip) and if they
> had truely done away with some more Motorola-like CISC
> instructions, it would really have pulled it off as a true RISC-design.
>
> Sipke de Wal
>
> ----------------------------------------------------------------
> http://xgistor.ath.cx
> ----------------------------------------------------------------
>
> ----- Original Message -----
> From: Richard Erlacher <edick_at_idcomm.com>
> To: <classiccmp_at_classiccmp.org>
> Sent: Thursday, December 20, 2001 5:42 PM
> Subject: Re: 6502/Z80 speed comparison (was MITS 2SIO serial chip?)
>
>
> > There are lots of things that you could compare, but the first things you've
> got
> > to leave out are the ones that aren't a Z80, which immediately deletes the
> Z180,
> > and Z280. The Z80 is not around any more than the 6502 is around. There
are
> > derivatives of the 6502 still in production, but they are few. There are
> > derivative of the Z80 being produced as well. None of the former are
6502's,
> > and none of the latter are Z80's.
> >
> > Your're right, in that they use their time differently. Because of the vast
> > architectural differences, one has to be cautious about chosing a
comparison.
> > The first basis, before chosing a set of instructions for a comparision,
> > however, is selection of an appropriate timebase. The Z80 uses its clock
> > differently than the 6502 does. The Z80 never uses fewer than 2 clock ticks
> for
> > a complete memory cycle, ant 2 ticks is only the lenght of the M1 cycle.
> That's
> > followed by the refresh cycle, during which, if I understand the process
> > correctly, the Z80 decodes that opcode. "Normal" memory cycles are three
> > clock-ticks in length, though only thwo of them are actually used during the
> > actual access of memory. The memory access portion of the M1 cycle is
> > essentially a
> >
> > The 6502 uses one clock tick for each CPU cycle. External hardware
determines
> > how long the memory access is, though the period beginning with valid
> addresses
> > and read/write begins just under half-way into phase-1 and continues
> throughout
> > phase-2, each of which is actually more-or-less half a clock cycle long. If
> you
> > don't attempt to do transparent memory sharing along the phase-1/phase-2
> > boundary, a memory cycle can be as long as 1-1/2 clock ticks.
> >
> > All of these constraints are based on the addition of no wait-states. The
Z80
> > has excellent support for wait-state insertion during any cycle other than
the
> > refresh cycle. The early NMOS 6502 supports wait state insertion on read
> cycles
> > only. There are ways of getting around this, but the Z80 certainly makes it
> > easier than does the 6502. CMOS 6502's support wait states on both read and
> > write cycles.
> >
> > If you run each of the two at a rate that allows each to use its shortest
> memory
> > cycle as the basic access window to memory, the 6502 will probably
outperform
> > the Z80 in a task that operates on 8-bit data in an 8-bit way. The more 16
or
> > 32-bit things you do, the more it favors the Z80, due to its inherent
features
> > such as the 16-bit registers and operatons on them without intervening
> > instruction fetches.
> >
> > If you compare the rate at which they operate, however, the 6502 has
features
> > that enable it to do 16-bit things quite handily in memory. Since one can
> view
> > the 6502's page-zero as an extended register set, with instructions
dedicated
> > for it. Those instructions include indirection into main memory, which make
> > 16-bit operations remarkably fast for a CPU that has no 16-bit registers.
> >
> > Have a look at it and contemplate that. It's a VERY clever design, intended
> to
> > make for a small, hence, cheap, CPU chip.
> >
> > Dick
> >
> > ----- Original Message -----
> > From: "Allison" <ajp166_at_bellatlantic.net>
> > To: <classiccmp_at_classiccmp.org>
> > Sent: Thursday, December 20, 2001 6:55 AM
> > Subject: Re: 6502/Z80 speed comparison (was MITS 2SIO serial chip?)
> >
> >
> > > Z80 uses it's time differently... Then again how many instuctions
> > > would it take to do a 16bit add (result in register or convenient place).
> > >
> > > The fact that both are still viable suggests they have adaquate
> > > speed and a rich enough instruction set to do many tasks.
> > >
> > > Last item, z80, Z180 and Z280 do not have the same timing.
> > > For example the Z280 can be run at a bus speed slower than
> > > the CPU speed and with the MMU and cache running in burst
> > > mode you get a very different bus utilization model.
> > >
> > > Generally the only things that count is:
> > >
> > > Can the cpu do the task?
> > > What cpu are you familiar with?
> > > What is the total cost to implement the task (firmware/software
counts)?
> > > Politcial impacts (company prefers, owns, has, used before).
> > >
> > > Do I think z80 is better than 6502? Yes, I'm biased. Is 6502 a good cpu?
> > > I think so, it certainly beat the 6800 and a lot of others in the 8bit
> > > space.
> > > Would I design with it? No, lack of experience, no on hand software base
> > > for it, limited tools to work with it. Would I consider it, likely.
> > >
> > > I have 6502, 6800, 1802, SC/MP, SC/MPII, ti9900, 8048/9/874x, 8080,
> > > 8085, z80, Z180 Z280, 6809 and T-11 to pick from. For a new design
> > > (personal) of some size say to run an OS then Z280 or T-11 for single chip
> > > I have 8748, 8749 and 8751s around. For simple controllers 8085 is easy
> > > to use if it grows out of the 8749. Then again I also have upd78pg11s
too.
> > >
> > Why do you see the 8085 as growing out of the 8049? The 8085 was quite
mature
> > when the 8049 came out, so they'r probably not from a common heritage, and
the
> > instruction sets are so totally different that one might believe they're
even
> > from a different manufacturer. The one that Intel claimed grew out of the
> > 8048/49 was the 8051.
> >
> > Of all these old-timers, that's the only one that still has life, and it has
> > LIFE in a big way! There are many variants, with the same common
instruction
> > set, but many different hardware features. The Dallas 89C420 runs at, 50
MIPS,
> > which certainly breathes life into the line. There are bit-banging things
> that
> > you can do with that one that few of the others above could handle in less
> than
> > 10x the time, yet the architecture supports a full 64K of data space and a
> full
> > 64K of code space, with memory mapped I/O in the data space.
> > >
> > <snip>
> > > >>
> > > >>
> > > >
> > >
> > >
> >
>
>
Received on Fri Dec 21 2001 - 00:22:27 GMT