Computer Chips from yesteryear

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Computer Chips from yesteryear

Post by lezanderson » 09 Jan 2015 17:03

When you look back at the early eighties computer you think of chunky ZX Spectrum Graphics and Beeps , ZAPs and other crude sound effects... but what really was avilable to computer designers.... money being no object...


Intel 8080/8085/8086
One of the first mainstream CPUs. This CPU is quite strange as it wasn't particularly very good even for it's day, but was used in the IBM PC and the rest is history..Spawned the 80286,80368,80486, Pentium etc, etc

The 6502
Being one of the cheapest CPUs at the time it was used in a lot of machines like the C64,Atari 800, BBC , ORIC etc etc..Simple internally and easy to source made it a common choice... was followed by the 65C816 as used in the SNES. These are still made today by Western Design Centre !

Probably the mot common CPU of the eighties, had several derivatives..HD64180, Z180,Z380 etc etc..still much used by hobbyists and homebrew builders. And I believe still in production in one form or another ?

Possibly the best 8 bit microprocessor of it's day..Not used other than the Tandy and Dragon computers, mainly due to it's high price.. followed by the HD6309 which is an enhanced version and pin compatible , making it a drop in replacement for a 6809 ! No longer in production.

TMS9900 & TMS9995
A Rare and unusual beast.. only used in the TI-99/4A, Tommy Tutor and Powertran Cortex (Home build) Machines? Had many advanced features for it's day as it was derived from a Mini-computer design. Quite Qerky with some idiosyncrasies. Not much used probably due to it's high price.. Well worth a look as it had an advanced design for it's day. No longer in production, can be found as NOS or Pulls also a VHDL model exists.

Motorola 68000
The Rolls-Royce of home micro CPUs.. used in the Atari ST, Amiga and Sinclair QL.. thought very cool at the time.

A Super-advanced design by ACORN used in the Archimedes computer range.. now lives on in most mobile phones and tablet like devices.

There are of course lots of other CPUs.. but they never really caught on the Z8000 to name one !

Sound Chips..

TI SN76480
A small an inexpensive sound Chip, commonly used in Z80 the Colecovision, Sord M5, and Memotech MTX. Can still be sourced very cheaply.

This was the sound chip used in the MSX machines, also used in the Amstrad CPC. A alter version YM2149 was used in the Atari ST. Still can be sourced

Phillips SAA1099.
This was a powerful and compact chip (DIP18) only used in the SAM COUPE. These can still be found quite easily and are cheap.

This was an advanced MSX+ Chip used in later MSX machines and Sound Card also used in some PC Cards.. Very powerful.. These can still be sourced today for $1.50 !!

Video Chips... It was mainly the crude and chunky graphics that defined early home Micros..let's see what chips where available !

The Thomson EF936x is a type of Graphic Display Processor (GDP). The chip could draw at 1 million pixels per second, which was relatively advanced for the year of its release (1982). Versions

Plastic or Ceramic

EF9365 512×512 (interlaced), 256×256, 128×128, 64×64
EF9366 512×256 (noninterlaced)
EF9367 1024×512
Also made SECAM Version for FRANCE


Integrated DRAM controller
Linedrawing, with delta-x and delta-y limited to 255 each. Support for solid, dotted, dashed and dotted/dashed lines.
Built-in 5×8 pixel ASCII font. Support for rendering tilted characters, and scaling by integer factors (of course no antialiasing)
Clear screen

The GPUs did not support direct access to the graphics memory, although a special command was provided to aid in implementing access to individual memory words.

The MC6845 and later R6545 where cheap enough to use in home micros like the BBC B, And Amstrad CPC.. at the time they where 'Cool' still used by a lot of homebrew designers !

The V6366 Was an ehhanced version , an evolution of the 6845, used in early PC Cards I beleive.

The TMS9929/V9938/V9958 needs no explanation , used in lots of Z80 systems, Namely MTX, MSX etx etc

The NEC 7220 / D72020
The High-Performance Graphics Display Controller 7220 (commonly µPD7220 or NEC 7220) is a video interface controller capable of drawing lines, circles, arcs, and character graphics to a bit-mapped display. It was developed by NEC and used in NEC's APC III computers, the optional graphics module for the DEC Rainbow, the Tulip System-1, and the Epson QX-10.[1]

The µPD7220 was one of the first implementations of a graphics display controller as a single Large Scale Integration (LSI) integrated circuit chip, enabling the design of low-cost, high-performance video graphics cards such as those from Number Nine Visual Technology. It became one of the best known of what became known as graphics processing units in the 1980s.

Amazingly all these chips are still avilable as legacy NOS or Pulls.. Chips like the EF936x and D7220 may of costs hundreds of dollars each back in their day.. but now only cost a fraction of that.

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Re: Computer Chips from yesteryear

Post by 1024MAK » 09 Jan 2015 23:45

Yes, yes, yes, no!!! :shock:

RAM :?

That is the thing. Lots of fast RAM was expensive. Add to that the costly video chips...
To enable easy, fast access, video RAM that was in part of the CPU's memory map was preferred. But that caused problems.

Now a CPU was not something that could be left out, and I think for the 1980's at least, the price difference between Z80's and 6502's was not significant.

But the different processors had to have different arrangements with the video system.

Plus, the lower clocked CPU's (1MHz 6502, 2.5MHz Z80 etc) were too slow to move high resolution detailed multicoloured graphics around in between the video system displaying the current video frame. Let alone also feeding the sound system and having some CPU processing time to run the game :(

Lots of tricks were used. Custom graphics chips in the C64 for example.

The Spectrum with low res. colour attributes. Plus many others...

Now? With what we have learnt, I think given the low cost of Z80 CPU's and low cost SRAM, I would go for having a number of different CPU's running the video, sound, keyboard/joysticks so that the "game" CPU could run the program. The video CPU could run at a fast clock, with fast RAM and interface to one of the video display processors. The main "game" CPU would also run fast (maybe a bit slower than the video CPU). The I/O CPU (for sound, keyboard, joystick, serial port, parallel port, network port, user port etc), would not need to run at such a high speed. This CPU could also control the FDD, HDD and CF or SD card for mass storage.

Oh dear, there I am dreaming again :lol:


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Re: Computer Chips from yesteryear

Post by Bill B » 10 Jan 2015 12:53

But then that is more or less what modern games machines (i.e. mobile phones) do. A main processer, a GPU and I/O chips.

See the Raspberry Pi (which is essentially an (obsolete) mobile phone chip) with an ARM main processor and the Video Core IV GPU.

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