Chip Counts of Various Z80 Machines

[mjelic]

I've been on a collection spree of all Z80 based machines and I'm nowhere near done, but I can already observe that the chip count of all this different machines varies greatly.

ZX Spectrum:  22
Amstrad CPC464: 25
MSX2: 48 (or so)
Microbee: 64 on the Premium Main board! Add another 40 on the Core board!

OK, so anyone care to have a discussion as to why and how they can be so varied? Is the chip count commensurate with capability?

(Please don't take this as any sort of criticism of any machine... I love them all. Z80 forever )

[Snuffytime]

The Spectrum and the Amstrad both use an ASIC/ULA which cuts down on a lot of discrete ICs while the MSX2 often has something similar but also has separate video RAM and maybe onboard FDD so needs some extra chips for that. The Microbee does not use an ASIC and was based on a number of individual S100 cards so is possibly less integrated.

[MbeeTech]

Custom IC's versus discrete logic is the reason for the higher chip count in the Microbee.
As a relatively small computer manufacturer, and less volumes than the likes of Commodore, Acorn, Sinclair etc.,
we just didn't have the budget to implement custom IC's.
It was a bit of a catch-22 though - custom IC implementation would have saved a lot of cost and made the machines
even more price competitive, however, the up-front R&D costs then had to be amortised across lower volumes pushing the
price back up.
The other drawback is that a new model (with new features) means another go at custom chips, and more Non-Recurring
Engineering costs.
That said, Custom IC implementation was considered back in 1986 but didn't go ahead for the reasons mentioned.

[Ernest]

Hi Mjelic,
You are correct in that the chip count will be based on capability in many aspects and as Snuffytime pointed out, the use of specialised integrated logic, which in some cases were almost a complete computer in a single chip. Primarily it will be dependent on when in the commercial computing cycle the unit was developed.
All the early Z80 systems use off the shelf logic to keep the development costs down, additionally most of the early systems were hand built. However as the idea of broad home use computers took off, large scale production, chip densities increases and the focus on mass production, the chip count dropped and the capabilities increased, all at the same time.

Focusing on the Microbee, as Snuffytime indicated the Microbee evolved from a S100 based computer into a kit that could be assembled by the home constructor and was initially all off the shelf components, excluding the case and power pack. When these were developed, the 2K Static RAM memory chip was the most economical that was available. As a result to get a 32KB system you needed 16 0.6" chips (quite a lot of real estate), however the advent of cheaper DRAM a few years later meant that twice the memory 64KB could be done in 8 0.3" chips taking up the real estate space of only 4 of the original chips.
Effectively this gave a 8 fold increase in memory density and a 2 fold decrease in chip count.
It was only a few years latter again and further 4 fold increase was seen in the memory capacity with no change of chip count with 256KB of memory in 8 chips taking up the same space that 4 of the original 2K chips, which only gave a total of 8KB.
In fact by this stage it was possible to purchase the SRAM slim 0.3" chips in high density which could achieve the original 32KB in a single chip half the width of the original 2K chip. A 16 fold reduction in chip count and half the board space, of just one of the original chips.

By this point right across the industry, much of the discrete logic was being replaced by either specialty large scale integration of gate into a single chip or Programable logic devices that could take the place of many individual logic components. In the case of the Microbee Programable logic was first introduced with the DRAM Coreboard and then use for the Premium and 256TC releases.

I have seen some imbedded (so no permanent human interface other than a serial terminal connection) Z80 systems from the late eighties with a chip count below 10, these still were using off the shelf components (no LSI chips or programable logic). If these were used I suspect the chip count could be as low as four. Further to that many industrial applications started to use Microcontrollers which effectively was a complete embedded computer in a single chip, CPU, memory (both RAM and mask programmed ROM), I/O control, timing even display and keypad input etc.

Ernest.

[CheshireNoir]

Popping in late to this thread: The MSX2 has a lot of additional onboard functionality. I built an Omega MSX 2 clone, and it really helps to understand what everything is when you build one.
MSX2 has: Onboard video chip with sprites, 128k of VRAM. Onboard Yamaha sound chip. 48k of ROM. 64k of main RAM. Often an FDC as well (Although my Omega didn't have one. I added it through the cartridge port)
Lots of glue logic to keep it all connected :-)

John

[ChickenMan]

Why not grab one of these https://www.tindie.com/products/circlem/...YoE6ZWxJc8  as it has less than 10 chips and running CP/M on a Z80 at about 180MHz.  Its also about the size of a Visa Card.

   

[someone]

Why not grab one of these https://www.tindie.com/products/circlem/...YoE6ZWxJc8  as it has less than 10 chips and running CP/M on a Z80 at about 180MHz.  Its also about the size of a Visa Card.

Someone has been using eZ80s & some Rabbit CPUs since their inception.  The eZ80's don't run at 180MHz, they can run up to 50MHz but with some single cycle instructions.
The official development module & evaluation kits are at:
Zilog eZ80 Acclaim!

Alternatively there's the Rabbit Z80 derivatives:
Rabbit

Someone's also got a Texas Instruments TI-84 Plus CE Calculator. It's a eZ80 with a graphical output and USB interface.
TI-84 Plus CE

Some programmers have ported and written some great programs for it.
TI 83 Plus CE Games

But if you do get one, make sure you don't get one with the most recent firmware that stops assembly language programs from being loaded apparently so students can't load cheat notes.