[HN Gopher] One-bit Computing at 60 Hertz
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One-bit Computing at 60 Hertz
Author : Tomte
Score : 29 points
Date : 2021-03-24 18:36 UTC (4 hours ago)
(HTM) web link (laughtonelectronics.com)
(TXT) w3m dump (laughtonelectronics.com)
| ctdonath wrote:
| For speculative fun, what's the fastest rate such a design could
| operate at? Are optical equivalent circuits reasonably possible
| (or some such)?
| CyberRabbi wrote:
| Old EPROMS are not very fast. 200 to 250ns access times were
| common back then, which would limit your clock rate to about
| 4Mhz or so. Of course you could use a modern NOR flash
| compatible pinout, which are about 70ns (~14MHz).
| simcop2387 wrote:
| This is why a lot of times you speed up embedded systems by
| loading the eeprom or flash data to ram, to avoid all the
| waiting by amortizing it at start up. A lot of times yiu can
| queue up the next but while waiting on the initial request,
| meaning you pay for a single wait and change on average in
| the end.
| CyberRabbi wrote:
| Very true, classic technique
| buescher wrote:
| Bravo. Reminiscent of the so-called Richards controller.
| https://en.wikipedia.org/wiki/Richards_controller
| CyberRabbi wrote:
| I wonder why the input from the mux has to be "deglitched." Is it
| due to noise or that the input lines are not synchronized with
| the clock?
|
| Also because it's going to a CMOS input you really need to watch
| the RC time constant. If it's too large, the input mosfets will
| both conduct for a relatively long period of time (called "shoot
| through") and may cause the IC to malfunction, potentially
| permanently.
|
| Also he has no discharge diode connected to the cap in that
| circuit, which could cause the cap to discharge damaging amounts
| of current through the IC on power down if the cap is relatively
| large.
|
| Also you have to make sure the resistor is large enough to avoid
| damaging inrush currents from the input mux to the cap.
|
| That RC filter really bothers me. Maybe it really is necessary to
| "deglitch" but if so he should really include the values he used
| because naively selecting rc values there will cause potentially
| serious errors. A Schmitt trigger buffer would be far less error
| prone.
| barbegal wrote:
| It's hard to analyse devices like this. It's clearly not Turing
| complete but it isn't a Turing machine. It can clearly compute
| any output for any given input (like a programmable logic array)
| but it can do a bit more given it can have several bits of
| internal state.
| Dylan16807 wrote:
| Turing machines are a minimal model that don't map easily to
| normal computers.
|
| This, on the other hand, is a very normal computer. It's just
| that it has an extremely small amount of memory. If you put a
| RAM chip between those output wires and input wires then it
| could be Turing complete.
| charcircuit wrote:
| RAM chips have finite memory. It still won't be Turing
| complete.
| freeone3000 wrote:
| Turing complete, in common usage, refers to the ability of
| finite Turing machines, not infinite ones, since any
| machine we physically built are built according to physical
| laws.
| dmitrygr wrote:
| It is a DFA plan and simple
| sm4rk0 wrote:
| https://web.archive.org/web/20210324184305/https://laughtone...
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(page generated 2021-03-24 23:01 UTC)