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Casio-F-91W die-shot

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Re: Casio-F-91W die-shot

#91

Post by leeoniya »

vasqw wrote: post #12

I bought one of those recently and I was surprised by how inaccurate it was. It drifted like 15 seconds every month. From what I've been reading, that is normal, but I was surprised - with all the technological advances that we have it is odd to think that cheap timekeeping is not a solved problem yet! Also: how is the software of these watches without a CPU designed? Is it something like Verilog or whatever?

my automatic Aqua Terra (8800 movement) maintains this (or better) accuracy, which i find astounding for a mechanical gear train that oscillates at 3.5Hz. i definitely would expect a well-tuned quartz movement to outperform this significantly. but i guess not for < $20 :p

Re: Casio-F-91W die-shot

#92

Post by stoppingin »

Apologies for a silly question, what exactly are we looking at here? I've seen the inside of an F-91W, and I always imagined that under the black epoxy blob was some kind of off-the-shelf microprocessor (most likely 4-bit) with a mask ROM containing the watch's logic. Is the entire watch run from this IC, with no processor? If so that's really interesting.

Re: Casio-F-91W die-shot

#93

Post by SnowHill9902 »

stoppingin wrote: post #92

Apologies for a silly question, what exactly are we looking at here? I've seen the inside of an F-91W, and I always imagined that under the black epoxy blob was some kind of off-the-shelf microprocessor (most likely 4-bit) with a mask ROM containing the watch's logic. Is the entire watch run from this IC, with no processor? If so that's really interesting.

If you are making millions of units for a RT application you definitely want custom silicon.

Re: Casio-F-91W die-shot

#94

Post by panza »

low_tech_punk wrote: post #90

From the business/design/technology POV, why is this watch so successful and so iconic?

It's durable, keeps good time, battery lasts 7-10 years, clear display, thin and light. It's incredible value for $15-25. Deserves to be as popular as it is.

Re: Casio-F-91W die-shot

#95

Post by gleenn »

vasqw wrote: post #12

I bought one of those recently and I was surprised by how inaccurate it was. It drifted like 15 seconds every month. From what I've been reading, that is normal, but I was surprised - with all the technological advances that we have it is odd to think that cheap timekeeping is not a solved problem yet! Also: how is the software of these watches without a CPU designed? Is it something like Verilog or whatever?

You might be surprised to learn a lot of servers even have largish time drift. I might be repeating info which is getting out of date but I heard 30 second drift isn't uncommon. Obviously doing NTP syncing more frequently would probably help that.

Re: Casio-F-91W die-shot

#96

Post by akdor1154 »

Tor3 wrote: post #25
vasqw wrote: post #12

I bought one of those recently and I was surprised by how inaccurate it was. It drifted like 15 seconds every month. From what I've been reading, that is normal, but I was surprised - with all the technological advances that we have it is odd to think that cheap timekeeping is not a solved problem yet! Also: how is the software of these watches without a CPU designed? Is it something like Verilog or whatever?

At around 1976-1977 I bought one of those fancy new LED wristwatches, where you pressed a button and the time lit up in red. Straight out of James Bond, as I recall. As I was studying electronics at the time I brought the watch to the lab and opened it and connected a frequency counter to the oscillator, you could clearly see the crystal and a little trimming pot (I don't remember by now if that was a pot or somethin…

> and the bus is there exactly on time

So that would locate you pretty unambiguously in Switzerland then?

Re: Casio-F-91W die-shot

#98

Post by tejohnso »

einpoklum wrote: post #45

F-91W is the watch I wear today. Actually, my favorite wristwatch - or rather the one I wore for 25 years or so - was a W-71. Unfortunately, you can't buy these except as vintage second-hand. I still don't understand why that is... I always felt it a more "aesthetically-balanced" version of the F-91W; plus it had 4 buttons rather than 3, which makes sense given the structure both watches. But I lost my W-71 while mov…

I don't wear watches as I'm always either at my computer or have my phone with me, but if I did wear a watch, I would probably go with something like the F-91W. Images of it bring on a nice retro nostalgia, and I appreciate its blatant function over flair aesthetic.

Re: Casio-F-91W die-shot

#99

Post by post-it »

gleenn wrote: post #95
vasqw wrote: post #12

I bought one of those recently and I was surprised by how inaccurate it was. It drifted like 15 seconds every month. From what I've been reading, that is normal, but I was surprised - with all the technological advances that we have it is odd to think that cheap timekeeping is not a solved problem yet! Also: how is the software of these watches without a CPU designed? Is it something like Verilog or whatever?

You might be surprised to learn a lot of servers even have largish time drift. I might be repeating info which is getting out of date but I heard 30 second drift isn't uncommon. Obviously doing NTP syncing more frequently would probably help that.

Yeah, the React Native debugger is broken on my Pixel because the time is different from my laptop by ~0.5 s, so short taps register as long presses or something like that.

Re: Casio-F-91W die-shot

#100

Post by iron2disulfide »

vasqw wrote: post #12

I bought one of those recently and I was surprised by how inaccurate it was. It drifted like 15 seconds every month. From what I've been reading, that is normal, but I was surprised - with all the technological advances that we have it is odd to think that cheap timekeeping is not a solved problem yet! Also: how is the software of these watches without a CPU designed? Is it something like Verilog or whatever?

The functionality of the F-91W is simple enough that I don't think a CPU would even be needed. Probably the digital parts of this chip are just state machines. That being said, the left half of the die shot looks like some kind of gigantic ROM, which could either be used by a CPU (as static program memory) or just transition logic/data for any generic state machine(s).

Verilog came out in 1984, but its use for synthesis (i.e. actually compiling text into circuits) was not popularized until much later, after correctness bugs in synthesizers and various other advancements in design tooling came around. It might have been used as a simulation/verification language for the digital portions of this chip.

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