homebrew 8008 project

[CP/M User]

"barryp" wrote:

>> The 99/4A would have came out later than the 99/4
>> though wouldn't it?

> Yes, of course.

>> Okay, so I mixed up the CPU as being the difference,
>> though I did know it was some hardware difference
>> about those machines. Unfortunately, the books I
>> have don't go into this very well, well since they were
>> mean't for the real hardware 'buffs.

> There are other minor differences too, not worth
> mentioning.

I'm guessing that those are cosmetic!

Cheers,
CP/M User.

 

[netbios]

Datapoint 2200

Datapoint 2200

"Erik" wrote:

> The Datapoint was a minicomputer, though. The Kenbak,
> the Scelbi and the Mark-8 were very early microcomputers.

So this is only a part of the machine then?

Cheers,
CP/M User.

The picture is indeed a complete Datapoint 2200 with a disk pack sitting on top. On the right top were two data tape cassette drives. The OS was loaded on one, and you used the other for your program store.

I programmed one of these in college, sometime around 1974~1976.
I wrote a program in assembly, yes it was 8008 compatible, that downloaded (via a serial port) form definitions and did data entry and then uploaded the results. This was tied into a hospital database system we were developing on a Cascade 80 minicomputer.

The Datapoint OS came with an editor and assembler and other program development tools and utilities. Since we wrote our own data entry application, I don't remember what else they had.

BTW: while you can make comments about the circuit technology deteriming whether something is a "mini" or a "micro" that can be misleading, particularly during cusps in the technology. A better deteriminate is the system I/O configuration and target application set.

Both this Datapoint 2220 and the Cascade 80 were built out of MSI TTL logic. The Cascade however was in a desk sized unit with a printing console, a line printer, and two disk drives (one removable).

Dave.

 

[Erik]

One of the Datapoint 2200s just sold on eBay for about $170 US (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=4121047707)

Not too bad a deal if you can find the boot tape or a copy. . .

Erik

 

[CP/M User]

Re: Datapoint 2200

Re: Datapoint 2200

"netbios" wrote:

> The picture is indeed a complete Datapoint
> 2200 with a disk pack sitting on top. On
> the right top were two data tape cassette
> drives. The OS was loaded on one, and
> you used the other for your program store.

> I programmed one of these in college,
> sometime around 1974~1976.
> I wrote a program in assembly, yes it was
> 8008 compatible, that downloaded (via a
> serial port) form definitions and did data
> entry and then uploaded the results. This
> was tied into a hospital database system
> we were developing on a Cascade 80
> minicomputer.

> The Datapoint OS came with an editor and
> assembler and other program
> development tools and utilities. Since we
> wrote our own data entry application, I
> don't remember what else they had.

> BTW: while you can make comments
> about the circuit technology deteriming
> whether something is a "mini" or a
> "micro" that can be misleading,
> particularly during cusps in the
> technology. A better deteriminate is the
> system I/O configuration and target
> application set.

> Both this Datapoint 2220 and the
> Cascade 80 were built out of MSI TTL logic.
> The Cascade however was in a desk sized
> unit with a printing console, a line printer,
> and two disk drives (one removable).

Thanks for your interesting comments Dave,
glad to see that someone has used one of
these machines & know what it's like. The
applications you've written sound failrly
impressive (even for this time)

Cheers,
CP/M User.

 

[CP/M User]

"Erik" wrote:

> One of the Datapoint 2200s just sold on
> eBay for about $170 US.

> Not too bad a deal if you can find the
> boot tape or a copy. . .

WOW!! Do they normally sell for more, Erik?

$170 US sounds fairly expensive, but I guess
it would be rarer to come by!

Cheers,
CP/M User.

 

[Allison]

"Erik" wrote:

> Speaking of oldcomputers.com, I really do like that site.


Instead they insist that the TI 99/4A came out in 1979
which is a mistake & that the TI 99/4A is a 16bit computer
& the TI 99/4 was an 8bit!


Cheers,
CP/M User.

The TI9900 (chip) is a 16 bitter, one of the first. The TI99/4 (and 4a) are based on the TI9900 chip and therefore 16bit. Now here's the twist as a cost reduction the 99/4 computer series had logic to trnaslate the 16bit data bus into two sequential 8bit reads/writes to 8 bit wide memory and IO. However the CPU is 16bit. The closest analogue to that is the intel 8086 and the 8088 as they are the same chip programatically but the bus interface differes. There are others that could do either 8 or 16bit such as the DEC T-11 wich was base PDP-11 on a single 40pin dip. The last odditiy for is the Z280 wich is really an 8bit (z80) cpu but has the ability to be either an 8bit bus or 16 bit bus for performance.

So it's easy for the non technical to not understand bus interface size and cpu data width.

Allison

 

[Allison]

The schematic for the internals for an 8008 is far logical only for Pmos logic and would not translate to TTL directly. It's about 5000 transistor equivelent to implement. For example most of the registers in the 8008 were not Flipflops but dynamic ram cells (it would crash if the closk was too slow).

To create a TTL design you will have to develope a functional specification and design from that. For the 8008 that should not be too bad as it was a pretty primitive device. What is more of a consideration is if you wnat the resulting TTL to result in a 18pin plug to the 8008 socket or if it can be a less of an emulation where its' interface to ram, IO and other logic is on an as needed basis. THe former is the more comples task as the 8008 had a multiplexed data bus where all the major control, address and data traveled in and out on those 8pins with te rest supplying clock, power and some state information.

Allison

 

[Allison]

Making your own processor out of TTL chips? Can you fill me in on what this is, like what TTL chips are and how the heck they can be made into a processor unit? You've perked my ears, hehe...

In the days before Microporcessor "Chips" the elements needed to create a computer were in more elmental forms. TTL is a logic family that is defines by levels and interchip interface rules. The TTL family contain basic logic elements and a few more complex ones but not enough to be a "computer" in itself. So it would take from 25-1000s of chips to create a "computer" with the number of chips required dependent on how complex a computer your trying to make.

Before TTL (around 1970ish) there was DTL and RTL logic families and then cards with raw transistors interconnected to yeild logic level functions.
For example a TTL NAND gate is rougly 5 transistors and 4 resistors.
There are famalies of logic that MOS (metal oxide gate) transistors as well
but the idea of package logic still applies despite differences in internal construction.

An example of a all transistor computer was the PDP-5 (1965) with the early PDP-8 (1967) being a mix of transistors and some early logic chip.
By 1976 the main logic of a PDP-8 was reduced to a single chip that contained enough transistors and internal "wiring" to do what the 1967
machine did.

Computers can be implemented with any device that exhibits two states and can be controlled to obey basic logic rules (AND, OR, NOT). In past years Tubes, Magnetic cores even neon lamps have been tried. Transistors and ICs based on transistors however proved most power efficient and durable over time. The only difference between ICs and transistors, is that transistors became smaller and then multiples on
one peice of silicon were interconnected to do what a board of transistors did. As techniques were developed and refined the number of transistors
and their assosciated interconnects reached the point where the 4004 and later 8008 chips were born. However the path to those chips had started years before.


Allison

 

[CP/M User]

"Allison" wrote:

>> Instead they insist that the TI 99/4A came out in 1979
>> which is a mistake & that the TI 99/4A is a 16bit computer
>> & the TI 99/4 was an 8bit!

> The TI9900 (chip) is a 16 bitter, one of the first. The TI99/4
> (and 4a) are based on the TI9900 chip and therefore 16bit.
> Now here's the twist as a cost reduction the 99/4 computer
> series had logic to trnaslate the 16bit data bus into two
> sequential 8bit reads/writes to 8 bit wide memory and IO.
> However the CPU is 16bit. The closest analogue to that is
> the intel 8086 and the 8088 as they are the same chip
> programatically but the bus interface differes. There are
> others that could do either 8 or 16bit such as the DEC T-11
> wich was base PDP-11 on a single 40pin dip. The last odditiy
> for is the Z280 wich is really an 8bit (z80) cpu but has the
> ability to be either an 8bit bus or 16 bit bus for performance.

> So it's easy for the non technical to not understand bus
> interface size and cpu data width.

Yes, I since come to realise the original TI 99/4 uses a 16bit processor while dealing with the 8bit reading & writing. Unfortunately, oldcomputers.com doesn't seem to acknowledge the two different machines - which is what I'm more fussed about. If you're into your Star Trek it's a bit like comparing Kirk's Enterprise & Enterprise A, they may look the same, but were two different ships (if you eliminate the cosmetic changes between movies!).

Cheers,
CP/M User.

 

[carlsson]

Now here's the twist as a cost reduction the 99/4 computer series had logic to trnaslate the 16bit data bus into two sequential 8bit reads/writes to 8 bit wide memory and IO.

I suppose there were other computers - minis and alike? - that used TMS9900 series to its full power? Would it have meant any improvement in sales of the TI99 computer if Texas Instruments had designed a more expensive machine from the beginning? How about a more powerful Basic, a more direct and 3rd party friendly way to expand the system etc? Probably they were ahead of their time. Would it not have been possible to compensate a little if the 99/4A model had become 99/5 with or without a 99/4 compatibility mode?

Oh well, all computer manufacturers did one thing or another "wrong" in retrospect. I guess it is a result of opening a new branch of trade.

 

[Terry Yager]

The TI 990-series were marketed as "mini-computers" even though they were small enough to sit comfortably on a desktop, and would prob'ly fit most people's definition of "micro-computer" by today's standards. Actually, I'm told that the TMS9900 chip is closer in archetecture to a mini-computer than to most micros.
When the 99s first came out, they were pretty expensive, till TI figgered out that the market wouldn't support a thousand-dollar home computer, and began drastically slashing the price in order to stay competitive with other home computers that were beginning to appear about that time.

--T

 

[barryp]

Now here's the twist as a cost reduction the 99/4 computer series had logic to trnaslate the 16bit data bus into two sequential 8bit reads/writes to 8 bit wide memory and IO.

I suppose there were other computers - minis and alike? - that used TMS9900 series to its full power? Would it have meant any improvement in sales of the TI99 computer if Texas Instruments had designed a more expensive machine from the beginning? How about a more powerful Basic, a more direct and 3rd party friendly way to expand the system etc? Probably they were ahead of their time. Would it not have been possible to compensate a little if the 99/4A model had become 99/5 with or without a 99/4 compatibility mode?

Actually there WAS a TI-99/5 (and, I think, a /6 and a /7) but the next most popular to the 99/4x was the TI-99/8, of which there are several in existance. That was to be "the next big thing".

 

[Allison]

The TI 990-series were marketed as "mini-computers" even though they were small enough to sit comfortably on a desktop, and would prob'ly fit most people's definition of "micro-computer" by today's standards. Actually, I'm told that the TMS9900 chip is closer in archetecture to a mini-computer than to most micros.
When the 99s first came out, they were pretty expensive, till TI figgered out that the market wouldn't support a thousand-dollar home computer, and began drastically slashing the price in order to stay competitive with other home computers that were beginning to appear about that time.

--T

The concept of minicomputers was from a time (mid 1960s) when computers wer typically 3 or more 6ft racks. Anything that would fit on
or under a desk was mini. For example in 1961 the PDP-1 was 4 6foot racks and that was the base CPU. By 1965 the PDP7 a later version of
the PDP-1 was half the size and many times faster. The PDP-8 family
started [ca1967] as typically a full rack in size [6 foot] and progressed down to a box of 0.5cuft (Decmate-III with floppy and hard disk). That trend was seens with nearly every vendor that was around long enough.

The later development of chips in some cases meant minicomputer versions of hardware could be reduced to a microcomputer chip or
set of chips. Examples are TI9900[TI990], 6100/6120[PDP-8], LSI-11. F-11,T11, J11[PDP-11], MicroVAX[32 bit VAX series went down to chips], uNova and Fairchild uFlame[DG nova] and no doubt I've missed a few.
With the reduction in the number of chips, smaller power needs and cooling the boxes got smaller. When they got small enough engineers started stuffing more into them.


Allison

 

[Allison]

The TI 990-series were marketed as "mini-computers" even though they were small enough to sit comfortably on a desktop, and would prob'ly fit most people's definition of "micro-computer" by today's standards. Actually, I'm told that the TMS9900 chip is closer in archetecture to a mini-computer than to most micros.
When the 99s first came out, they were pretty expensive, till TI figgered out that the market wouldn't support a thousand-dollar home computer, and began drastically slashing the price in order to stay competitive with other home computers that were beginning to appear about that time.

--T

Well the TI9900 is a minicomputer that was reduced to a chip. It's very minicomputer in the way it's interfaced. The Bit addressed IO was as odd
by micro standards as they come and the only other one that stands out as very mini is the 6100/6120 copying the PDP8 IO. If you look at micros designed orginally as micros rather than micros realized from mini designs
there are sometimes unique things that are very mini. Those oddities are
a result of the cost of putting IO on minis, IE: the printer or disk could cost more and have a higher chip count than the CPU.


Allison

 

[machine]

Computers built using TTL devices (the 74 and 54 series of TTL) was common prior to useful microprocessors. They are called 'Discrete Processors'.

But it is not an easy task to build your own discrete processor. It takes a lot of skill and it will take probably 200 to 400 chips. The board would be large and just making the PCB will cost a lot as it will be so large. Doing the PCB layout by hand will simply be practically impossible, you would need software to do this like Protel.

Most 'home brewers' use PAL chips which contain huge numbers of uncommitted gates in one chip. They write the software to implement their particular computer design in the chip and programming hardware programs the PAL chip's gates in a particular fashion resulting in a home built microprocessor. There's quite a few hobbyists doing home brews. But even doing it in PAL chips is very skilled work.

You would need to know how to implement 'microcode' also which is the code embedded in all microprocessors which tells the chip how to behave internally. Microcode is not the program you apply externally to the microprocessor to get it to do useful things.

 

[Allison]

Computers built using TTL devices (the 74 and 54 series of TTL) was common prior to useful microprocessors. They are called 'Discrete Processors'.

But it is not an easy task to build your own discrete processor. It takes a lot of skill and it will take probably 200 to 400 chips. The board would be large and just making the PCB will cost a lot as it will be so large. Doing the PCB layout by hand will simply be practically impossible, you would need software to do this like Protel.

Humm, I did it and it was less than 200 chips. A really interesting design was EGO presented in BYTE Sept 1985, a 16 bit machine. It used no PALS
and the densest devices (other than rams) were 74381 ALU and 74189
register array. Rough guess is under 100 TTL packages. It's not microcoded.

I have a very crude machine I did in less than 50 chips. Didn't have Protel nor use it. The base design is 16bit word and a vague resemblence to PDP-8 but a few things like the Data counters in ram left out. All ttl and
fast 400ns fetch/execute cycle. No gals/pals no microcode. Paper,
Logic maps, And the TTL data book.

There are several minimalist CPU designs like TOY, VSC and others. See
http://www.homebrewcpu.com/links.htm One desing listed was only 16
pieces of logic if PALs are not used. Granted it's a trivial machine but
if you can conceive and program that Colossis is just a big wirewrap
project away.

You would need to know how to implement 'microcode' also which is the code embedded in all microprocessors which tells the chip how to behave internally. Microcode is not the program you apply externally to the microprocessor to get it to do useful things.

Microcode once you understand the simplest forms is trivial and can be
easier than a sequence engine. However it's not required. The upside of microcode is it can be easier to move bits than wires. The simplest uCode
machine is two parts. A clock source like a 555 timer chip, 74374 octal latch and a EPROM of atleast 256x8 in size. Code optional. Using just a pair of 374s and a 2732 I can easily make a state machine that can alter it's state based on inputs. Thats the core of a programable system.

I once believed as an engineer designing computers was black art. One day I decide to found out how they work and found out that taken one step at a time they are less forbidding than many say. What was missing for me was all those tutorials of how gates and FFs work were only a prelude
and then they skipped over how sequential systems happen to work. Computers are only very big sequential systems and in some cases
sequential systems within larger sequential systems. The latter being
very terse descritption of a microcoded computer.


Allison

 

[machine]

"Microcode once you understand the simplest forms is trivial and can be easier than a sequence engine. However it's not required."

No processor discrete or integrated can run without microcode. Microcode is NOT trivial. Microcode controls the entire processor's functioning. Very few engineers produce microcode. It is a rare skill.

For every function there will be up to 100 switches enabled. A discrete processor will typically have 30 or more functions.

 

[Allison]

"Microcode once you understand the simplest forms is trivial and can be easier than a sequence engine. However it's not required."

No processor discrete or integrated can run without microcode. Microcode is NOT trivial. Microcode controls the entire processor's functioning. Very few engineers produce microcode. It is a rare skill.

For every function there will be up to 100 switches enabled. A discrete processor will typically have 30 or more functions.

Well, your wrong. Sure there are a lot of thing going on in a machine
but they can be digested easily and understood once you have the basics clear.

There are two ways to implment the control system thats the core of a computer. One being a microcoded state machine and the other is a
sequential machine. They are very differnt in design, construction and even the debugging process s different.

RCA1802 is not microcoded
PDP-8 is not microcoded.
Z80 is not microcoded
PDP-11 in the LSI-11 form is microcoded
most other PDP-11s are sequential
VAX is microcoded
EGOII (sept 1985 p229, Byte magazine is a sequential machine)

TOY (a teaching design) has been rendered in both a sequential
and micro coded forms. Byte had an article showing the design of both.

Shall I go on.. There are no shortage of examples.

Generally speaking a two state RISC machine is less likely ot be microcoded than a CISC machine. That however is not absolute. There are trade offs for both styles of design.

Microcode is easier than doing a 22 state sequential machine. I've done both.

Microcoding and sequential machine programmers are not rare, they are
just not noticed anymore. With FPGAs and CPLDs being so cheap and dense every CSEE student has to do a processor implmentation of some sort these days as a lab project. There are a lot of students. The other part of it is with logic so plentyful figuring out how to save a package or
two doesn't compute so long as it all fits in the selected CPLD or FPGA.

I've studied some of the simplest examples as well as the complex. I've been designed and built a few of both over the last 30+ years. The simplest microcode engine I've done was less than 8 peices of common 1980s TTL and a 8bit wide by 256 byte PROM. It isn't a pentium but the principles remain visible.


Allison

 

[ka7ftp]

Homebuilt 8008

Homebuilt 8008

Here is complete info to build an 8008 computer.

len

http://www.8008chron.com/

 

[Chris2005]

FWIW there's a book by Robert Grossblatt (perhaps pardon the spelling) that details the description of an 8088 version of a similar thing. Called "the 8088 Project Book". Probably could be found on Amazon for next to nothing.