Is anyone interested with the Z80?

Did you know that the Z80 has different memory access timings for instruction fetches and standard memory accesses?

I worked at Mostek maintaining the Fairchild Sentry testers used to test the Z80s when they first began to manufacturer them. The second computer I every

built (parts, pcb, solder) was the SDB-80 which was the Mostek Software Development Board for the Z80 with 16K bytes (8 - MK4116 16K bit) dynamic RAMs

which Mostek also made. The first wire wrap board I ever made was a 48K byte dynamic RAM board also using MK4116s that worked with the SDB-80. I can

tell you there were a bunch of happy technicians when we were told that Mostek would be second sourcing the Z-80 and even happier when we were told we

could buy SDB-80 kits and build them ourselves! Those were really fun days. I still have a Zilog Z80 in a ceramic package that says it was manufactured in

Dallas even though Mostek was actually in Carrollton a suburb in Dallas County just north of north-west Dallas.

Hi COMPACT and Doug,

While the PC-1600 just didn't take off in the second half of the eighties, Sharp out of the blue discontinued the whole PC-1500A line. Among the

large number of commercial users worldwide with business application programs, one company especially had a huge practical problem with that:

Allianz, Germany's largest insurance company. They had abt. 50.000 (no typo !) PC-1500A systems for their commercial field service - now to be

written off just like that !

An other, very small, German company, having invested heavily in a rather unique application, decided, they could perhaps ensure continuity by

purchasing several dozen used systems from Allianz. Thus in the aftermath of the PC-1500A era a remarkable opportunity presented itself for us

(i.e. me and my son). Weilekes also was a father & son operation, who had devised a corrosion testing system for oil and gas pipes, to be used

in Siberia. The PC-1500A system was choosen because of its virtual indestructability and reliability in harsh environments. If anything, the mate

to the pocket computer - in fact a tiny 4-color plotter with system I/F - had to be overhauled meticulously. And that's where we came in.

My son (15 at the time) had already done so with several of these cigarette-pack size little gems*. Next the NiCad pack had to be exchanged for

a 'real' Sanyo (ask any model 'copter builder !). PC-1500A got a new keyboard switch mat, and any worn-out keys were replaced**. Refurbishing

further included all connectors, scratched LCD windows - sometimes complete cases were replaced.

Together with the Weilekes custom unit, the pocket computer + plotter were built into a special sort of cradle that the user wore like a candy seller

in a movie theatre; except this one had to shield the equipment from Siberian climate ... Sensors connected to the cradle were used for the actual

measurements. I believe these were basically resistance measurements - not surprisingly, taking into account the prominent position of German

developpers in skin resistance measuring medical devices.

What puzzles me now (was'nt aware of this then): both the former Soviet Union, and Hungary produced their own PC-1500A clone at the time;

wasn't Gazprom aware, or didn't they care ...?

Cheers

Ray

*of the Japanese ALPS brand, these days famous a.o. for its high-end audio-grade potentiometers

**Sharp spare part sets with only the [SPACE] and [ENTER] keys came in very handy indeed

I like your posts. They're fascinating!!

I wholly agree!

Thank you, COMPACT and Andrew Johnson !

Think I'm just privileged, having lived (better still: mostly had my youth in) the era of:

- the birth of the micropocessor

- the development from calculators into hand-held computers

- the 'transistorizing' of electronics

- the chip revolution leading to "zero cost electronics" (Scientific American, 1975), and ultimately to hand-held communication devices

- the development of LCD and similar display technology

and so on ...

It all began when awed by a self-built X-tal receiver, while visiting a cousin - almost mystically fascinating !

Not only did I blend together one myself shortly after, but also began reading books on radio history from the school library (which didn't have

anything DIY). And I got pretty jealous of inquisitive people like myself, who had been lucky enough to live during the age of say Heinrich Hertz,

Marconi, and the like (unfortunately I discovered Tesla much later). So obviously, some people just cannot be pleased enough ... !

Cheers

Ray

P.S.: the excitement of listening to your self-built X-tal receiver is similar to watching your first program do what you envisioned;

        in both cases, "you'll always remember your first time" ...

Come to think of it: I've also been privileged to live in the era of:

- the dawn of music registration on vinyl

- the transition (soon after) from mono to stereo

- transistors displacing vacuum tubes (while becoming a swiftly expanding family)

- the invasion of digital technology in the art of music registration and reproduction, culminating in the CD, but :

x NO, don't feel privileged, having to witness music quality being slaughtered by ease-of-use driven technology,

   like MP3, streaming, and what have you ? (Microsoft 'eliminated' prof. Johnsons's HDCD, the best digital format ever).

So, I feel privileged, being able to enjoy in the same lifetime:

- the unsurpassed vibrancy of shellac disc mechanical replay with horn reproduction (thank you Canned Heat for pointing that out, back stage !)

- the reappreciation of mono recordings and revival of mono music reproduction (even newly developed vinyl cartridges)

- the vacuum tube revival (thanks mainly to Russia, China, and Eastern Europe - with NOS running out)

- the reappreciation of pure Red Book, but moreover of analog audio in all its forms.

How come ?

Organizers gradually took over the pocket computer market, but mid nineties my son helped me realize, there was an end to this.

His expertise (my former hobby) was (still is) high quality audio. So we decided to start our own import company - later developping

proprietary products.

What's the point in all of this ?

In one word: digital ! While digital control of equipment functions is only remotely (pun intended) interesting, we focussed on DSP,

digital signal processing. At first I was somewhat puzzled by the notion of losses in file conversion and transition - never encountered

such problems while processing data files on a computer !  Admittedly, it took me some time to figure out the cause.

Anyway, let me end this 'chapter' with a cliff-hanging anecdote:

After we were asked frequently by the public, why we did not demonstrate with digital equipment at an audio show, we got tired of lengthy

answers, followed by ditto discussions. So we devised a 'cunning plan': a large poster of the Mona Lisa was fed through a shredder, which

we stopped just before the end was reached (if this seems familiar to you, having followed the news lately: we were fisrt !). Next we 'repaired'

the poster with transparent 'magic tape'; then with a felt pen we wrote under the picture: "NICE, ISN'T IT: DIGITAL ?". Problem solved ...

Cheers

Ray

Reading this reminds me of how old I am. Even dirt seems young these days.

Clem

Hi Clem (if that's alright with you ?),

Don't despair, I've become a 'grumpy old man' myself lately sometimes -:).

(My wife was born in the middle of WW II, glad I missed that period - if only just).

But writing about my experiences gives me the idea that it isn't all over, and of no use to anybody any more.

If I can fill in some white spots in other members' memories and/or knowledge, like they have done in mine,

that would make it worth my while (like they said in the old days). Just keeping readers amused is OK too, btw.

I had to stop my electronics experiments a few years ago because of deteriorating eyesight. SPICE for me is no alternative, as I believe it can not

reliably simulate a real novelty circuit. After all it stands to reason that you can't get out what has not been put in, can you ?

So the only thing left for me to do is devising new circuits ... mentally, and hoping I can get someone interested enough to put my ideas to the test.

Also rewarding is acting as a kind of sparring partner for my son, when he is figuring out, how to improve on existing vinyl cartridge cantilever

design e.g..

Hope I haven't annoyed you.

Cheers

Ray

As for degrading eyesight I'm reliant upon my bench binocular microscope just to solder 1960's tech like DIP ICs and through hole.

My spare parts are so old that I have to remove the unwanted oxide layer from them (just like my brain).

I don't like too much SPICE in my food.

Analog turntables - Don't get me started!  The analog signal is distorted prior to recording so it can be reverse distorted for playback to support the RIAA equalisation.

And also seem to also ignore other distortion influences such as wow and flutter, stylus/cartridge momentum and contact friction variations

Like oscilloscopes, sound should be sampled at about 5x or more than the desired maximum bandwidth.

And how does one get a speaker to playback perfect square waves?

All of this gives me the "jitters!"

Hi Andrew,

Reading your profile, several thoughts spring to mind:

- seems like a wonderfulfilling (language economy) job/passtime - educating people, in order to enrich nowdays' ict with an intriguing past

- visiting my wife's family in Canada years ago, we went to the Toronto Science Museum - I had the time of my life !

- your level denominator goes, well ... lovely with your 'job' -:)  Women's role in technology is grossly underrated, and almost neglected

  (ENIAC, NASA, etc).

Cheers

Ray

To the list of analog turntables (and vinyl records) problems vs CD you can add  poor channel separation, lower signal to noise, far less dynamic range, low frequency limits,

groove wear, warping, inherent vulnerability to acoustic feedback, tracking problems, and less resistant to injury and corruption.

As for reproducing square waves, as far as I know, no instrument other than electronic synthesizers produce anything that approaches the fast rise/fall times of a square wave.

That said, there are several groups that I like that use(d) synthesizers.

To the list of analog turntables (and vinyl records) problems vs CD you can add  poor channel separation, lower signal to noise, far less dynamic range, low frequency limits,

groove wear, warping, inherent vulnerability to acoustic feedback, tracking problems, and less resistant to injury and corruption.

As for reproducing square waves, as far as I know, no instrument other than electronic synthesizers produce anything that approaches the fast rise/fall times of a square wave.

That said, there are several groups that I like that use(d) synthesizers.