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From: cs_posting on 6 May 2008 11:15
On May 6, 9:24 am, rickman <gnu...(a)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.

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.
From: Tomás Ó hÉilidhe on 6 May 2008 12:19
On May 6, 4:03 pm, cs_post...(a)hotmail.com wrote:
> On May 5, 5:12 pm, Tomás Ó hÉilidhe <t...(a)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).
From: linnix on 6 May 2008 12:27
On May 6, 9:19 am, Tomás Ó hÉilidhe <t...(a)lavabit.com> wrote:
> On May 6, 4:03 pm, cs_post...(a)hotmail.com wrote:
>
> > On May 5, 5:12 pm, Tomás Ó hÉilidhe <t...(a)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).

If you did it right for the display, you can free up more than one pin
for the shift register.
From: cs_posting on 6 May 2008 12:48
On May 6, 12:19 pm, Tomás Ó hÉilidhe <t...(a)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).

No, if you do it right only one pin is needed to clock the pair of
shifters.

However, with either this scheme or the binary counter and decoder you
proposed,
you may find you need a reset or an input back to the uC to
synchronize the software with the display ;-)
From: rickman on 7 May 2008 00:06
On May 6, 11:15 am, cs_post...(a)hotmail.com wrote:
> On May 6, 9:24 am, rickman <gnu...(a)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.

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