Simple Clockable Decoder Chip

Tom�s � h�ilidhe wrote:
> 
> Only one pin is needed from the microcontroller.
> 
> With the shift register setup, two pins are needed (one for clock, one
> for data input).

You can make a vanilla OneWire Shift-Register interface, by using a
RC on the Data pin, and pulse-width varying the clock.

Assuming a Positive edge Clock :

A narrow clock Low time, loads a HI on the rising edge
(D Pin is still hi),
a Wider clock LOW time, loads a LOW on the rising edge
(D pin has had time to follow the clock Lo)

Shft registers are very common, and you have a choice of drive-currents.

-jg

rickman wrote:

> What is your cost limit?  CPLDs are pretty cheap.  I want to say I
> have seen devices for around a dollar US.  Even obsolete logic chips
> aren't much cheaper than that.
> 
> Is this intended to teach you something?  If so, I would *require* you
> to use a CPLD if I were the instructor.  There is very little value in
> learning to use chips that were designed long before the PC.  Does
> your instructor also ask you to use a dial phone?  Do you connect to
> your computer using a TTY?  (do you know what a TTY is?)

The 4017 candiate is appx 15c in moderate volumes, and has uA standby 
power, and a small, easily handled package, and 5V operation (so can 
drive Power MOSFETS). It is in volume production, so is not an
obsolete device.
(not all 4xxx devices are obsolete)

If that is ALL the functionality that is needed, then a CPLD
could be a massive overkill.

If the 4017 does not make it, and you need to add more chips, then
a CPLD moves onto the radar.

Avoid the high power ones, and for low power/low voltage designs
look at ATF1502BE/XC2C32A/MACH40xxZE series.

If you need to drive 5V from a low power CPLD, things get tougher...
(that's one combination that has fallen-thru-the-cracks, and another
reason those 4xxx / HCxx  series devices still sell in volumes ! )

In fact, many 4xxx devices leave CPLD for dead, on a production 
life-time basis !

So, a well rained designer knows about CPLD _and_ Logic Devices, even
back to 4000 series ones.

-jg

On May 6, 11:15 am, cs_post...@hotmail.com wrote:
> On May 6, 9:24 am, rickman <gnu...@gmail.com> wrote:
>
> > Is this intended to teach you something?  If so, I would *require* you
> > to use a CPLD if I were the instructor.  There is very little value in
> > learning to use chips that were designed long before the PC.  Does
> > your instructor also ask you to use a dial phone?  Do you connect to
> > your computer using a TTY?  (do you know what a TTY is?)
>
> If there's a part available off the shelf for 10 cents, that's likely
> going to
> beat the programmable logic solution in most cases.
>
> Where it won't is if you don't have those, or don't want to stock
> them, and
> go through small CPLD's like jelly beans.  Then the cost of
> programming
> the CPLDs might possibly beat the cost of inventory.
>
> Or if the 10 cent part (or pair of them) won't do the whole job.  If
> you need the
> CPLD anyway, then this function is no longer the justification for it.
>
> But usually, if you can buy your whole solution, it's better to do
> that than
> make a custom one.  And for that reason, a lot of old technology chips
> survive, albeit in often in smaller modern packages.  There's just no
> reason
> to drop them.

Maybe your designs are different from mine.  I just did a design and
the only logic part on the board is an inverter which is only there to
invert a control line so it can be used to program the PLD.  I
literally can't remember the last design I did that didn't have a PLD
of some sort.  In fact, the only design I have *seen* in the last five
years that used an SSI or MSI part (other than a single gate) was a
controller board that used a keypad encoder.  I was involved because
we were told the part would be going EOL within a year.  So we
designed it out.

When you say "a lot" of older chips survive, I think the variety is
pretty limited.  I can't imagine that a part like this will continue
indefinitely.  The buffers, counters a shift register or two and
multiplexers will be about the only parts left before too long.
Although there are companies that specialize in obsolete chips.  I
guess these parts may live on though those channels.


> Rotary dial phones?  They had some real issues (finger hurt really
> badly trying to
> win radio station call in prizes).  TTY?   Well, I use software
> emulation of one
> almost every day...  that basic idea is sound, but printing on paper
> isn't usually needed.

Yeah, that's kinda the point.  The concept is still relevant, but the
actual TTY was extinct a long time ago.  Heck I gave away an LSI
terminal (completely designed out of MSI) years ago that I had paid
$400 for used... along with my LSI-11 (kinda wish I had kept that one)
and a bunch of other stuff.  I did keep my 6502 trainer board with the
hex keypad, but I haven't seen it in years.  I guess I don't really
have a lot of call for it.  :^)

I do still have an 8008 computer around here somewhere, along with
documentation.  I think I promised it to someone who was making a sort
of museum for himself.  I never got around to shipping it out, I guess
I just don't really want to part with it.

MSI is dead, long live MSI.

On May 6, 12:19 pm, Tom=E1s =D3 h=C9ilidhe <t...@lavabit.com> wrote:
> On May 6, 4:03 pm, cs_post...@hotmail.com wrote:
>
> > On May 5, 5:12 pm, Tom=E1s =D3 h=C9ilidhe <t...@lavabit.com> wrote:
>
> > > As I said elsethread, I've decided to run a 4-Bit counter into a 4-
> > > to-16 decoder.
>
> > In what way is that superior to daisy chaining two shift-register type
> > devices?
>
> Only one pin is needed from the microcontroller.
>
> With the shift register setup, two pins are needed (one for clock, one
> for data input).

We've had this conversation before.  You can use an RC with one
control signal, similar to the other kludge... I mean *design* you did
with two RCs.  The RC will stop the short pulses from reaching the
data pin.  So you can hold a level for a bit to allow the data pin to
establish a state and then give it a fast pulse to clock the data in.
I think your design used an RC to hold the input to a one or something
like that so the part would set up with a single one bit and the rest
zeros.  Then it was clocked with feedback so the one circulated
forever.  But maybe I am not remembering correctly.

Grant Edwards wrote:

> On 2008-05-06, Eric Smith <eric@brouhaha.com> wrote:
> 
>>Tom??s ?? h??ilidhe wrote:
>>
>>>As I said elsethread, I've decided to run a 4-Bit counter into a 4-
>>>to-16 decoder.
>>
>>That will work fine, as long as you don't mind the decoding glitches.
> 
> 
> Or as long as he uses a gray-code counter.  You can buy gray
> code counters, can't you?

Not as a mainstream part. Trivial in a SPLD.
What you CAN do, is use a narrow clock, and feed that into the
Decoder ENABLE pin, so you blank between states.
With driver-delays this can help prevent ghosting effects.
-jg