Reply by Paul Keinanen April 24, 20042004-04-24
On Thu, 22 Apr 2004 12:20:55 -0400, Ben Bradley
<ben_nospam_bradley@mindspring.example.com> wrote:


>>You could do it with a string of one-shots, but >>I feel guilty just suggesting such a grotesque >>kludge. > > I thought of that too, it seems like an interesting if a bit >bizarre design exercise, but I didn't mention it because the post >smells too much like a homework/class assignment.
I guess giving "impossible" homework and watching what kind of stories the students put on the internet and what discussion this will cause might be fun to watch :-). While a string of multivibrators or delay lines are simply to generate a serial stream of serial stream of bits with some badly defined rate (+/- 20 %) and gating the start bit through a similar chain of multivibrators (with as bad tolerances) on receive might give not so impressive results. Since it was not stated if this had to be done in silicon, I would suggest looking at how the original Teletypes did it with rotating shafts and electromagnets. These devices were fully electro mechanical and in some more modern versions the only transistor was in the 20 mA constant current source, but the serdes part was fully electro-mechanical. Of course, some may claim that the constant rotating speed of the shaft was a clock, but on the other hand, as someone suggested using a delay line to loop back the pulse, this also sounds like a delay line oscillator and hence a clock. Paul
Reply by rickman April 24, 20042004-04-24
Shashi wrote:
> > Hi, > I'm doing a project in clockless uart..as u know that the primary > function of uart is parallel to serial conversion while transmitting > and serial to paralel conversion while receiving..I was wondering if > someone could tell me as how can i do a parallel to serial conversion > and vice versa without using a clock. > > Note: This is a circuit whoch doesnt use a clock at all/ Asynchronous > Circuit/Clockless Circuit.
I belive this was also posted to comp.arch.fpga. A UART sends data bit serial with a given period per bit. So the signal must sampled on a timed basis in order to read the bits after synchronizing with the start bit. Normally a clock is used to provide the timing, but there are other ways. A tapped delay line can be used to delay the input signal. The start bit can be detected at the end of the delay line and the data bits are read at each of the bit taps. Once a start bit is detected, the start bit detection must be disabled for one full character time. This would be a very difficult circuit to design. But it could be done. -- Rick "rickman" Collins rick.collins@XYarius.com Ignore the reply address. To email me use the above address with the XY removed. Arius - A Signal Processing Solutions Company Specializing in DSP and FPGA design URL http://www.arius.com 4 King Ave 301-682-7772 Voice Frederick, MD 21701-3110 301-682-7666 FAX
Reply by Hans-Bernhard Broeker April 22, 20042004-04-22
Shashi <shashi22k@rediffmail.com> wrote:

> I'm doing a project in clockless uart..as u know that the primary > function of uart is parallel to serial conversion while transmitting > and serial to paralel conversion while receiving..I was wondering if > someone could tell me as how can i do a parallel to serial conversion > and vice versa without using a clock.
I sense a serious case of "target conflict" here. As in: trying to make omeletts without harming roughly elliptical hulls of reproductive products of certain species of birds (vulgo: eggs). Serial protocol means that bits travel on the same line, separated by nothing but time. So you *will* need some gadget in your circuit that measures or controls time. Such a gadget is called a clock. Ergo: you *will* need a clock to generate any serial protocol. That leaves only one reasonable way to sneak out of your conflicting goals: you could have the clock elsewhere, i.e. in the communication node at the other end of that serial line (and pray that your clockless circuit is fast enough to keep up with the forced external clock).
> Note: This is a circuit whoch doesnt use a clock at all/ Asynchronous > Circuit/Clockless Circuit.
Then you'll have to put one in to drive the UART. -- Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de) Even if all the snow were burnt, ashes would remain.
Reply by Jim Stewart April 22, 20042004-04-22
Ben Bradley wrote:
> In comp.arch.embedded, Jim Stewart <jstewart@jkmicro.com> wrote: > > >>Shashi wrote: >> >>>Hi, >>>I'm doing a project in clockless uart..as u know that the primary >>>function of uart is parallel to serial conversion while transmitting >>>and serial to paralel conversion while receiving..I was wondering if >>>someone could tell me as how can i do a parallel to serial conversion >>>and vice versa without using a clock. >>> >>>Note: This is a circuit whoch doesnt use a clock at all/ Asynchronous >>>Circuit/Clockless Circuit. >> >>You could do it with a string of one-shots, but >>I feel guilty just suggesting such a grotesque >>kludge. > > > I thought of that too, it seems like an interesting if a bit > bizarre design exercise, but I didn't mention it because the post > smells too much like a homework/class assignment.
I know. It is sad because the first computer I *really* understood was the PDP 8/l, which was a totally asyncronous design. Ironically, the only clock in the machine was for the tty "uart". If the machine broke in such a way as to stop the propagation of pulses, you had no way to scope anything. One of the tricks was to jumper the uart clock to the start key so you could poke around and find out where the pulse was getting lost.
Reply by Ben Bradley April 22, 20042004-04-22
In comp.arch.embedded, Jim Stewart <jstewart@jkmicro.com> wrote:

>Shashi wrote: >> Hi, >> I'm doing a project in clockless uart..as u know that the primary >> function of uart is parallel to serial conversion while transmitting >> and serial to paralel conversion while receiving..I was wondering if >> someone could tell me as how can i do a parallel to serial conversion >> and vice versa without using a clock. >> >> Note: This is a circuit whoch doesnt use a clock at all/ Asynchronous >> Circuit/Clockless Circuit. > >You could do it with a string of one-shots, but >I feel guilty just suggesting such a grotesque >kludge.
I thought of that too, it seems like an interesting if a bit bizarre design exercise, but I didn't mention it because the post smells too much like a homework/class assignment.
>I just put my finger down my throat and now I >feel much better.
Reply by Anthony Wong April 22, 20042004-04-22
"Shashi" <shashi22k@rediffmail.com> wrote in message
news:7cdabebf.0404211144.38da229c@posting.google.com...
> Hi, > I'm doing a project in clockless uart..as u know that the primary > function of uart is parallel to serial conversion while transmitting > and serial to paralel conversion while receiving..I was wondering if > someone could tell me as how can i do a parallel to serial conversion > and vice versa without using a clock. > > Note: This is a circuit whoch doesnt use a clock at all/ Asynchronous > Circuit/Clockless Circuit. > > Thank You > SHASHI
If you're not trying to do an RS232 standard UART, you could use another standard that includes the clock in the data stream. There many other standards that allow you to derive the clock from the data stream. Or, did you mean an auto-bauding UART? Where the UART can derive the baud rate based on the assumption that it is receiving the characters "AT"? --Anthony
Reply by moocowmoo April 22, 20042004-04-22
"Shashi" <shashi22k@rediffmail.com> wrote in message
news:7cdabebf.0404211144.38da229c@posting.google.com...
> Hi, > I'm doing a project in clockless uart..as u know that the primary > function of uart is parallel to serial conversion while transmitting > and serial to paralel conversion while receiving..I was wondering if > someone could tell me as how can i do a parallel to serial conversion > and vice versa without using a clock. > > Note: This is a circuit whoch doesnt use a clock at all/ Asynchronous > Circuit/Clockless Circuit. > > Thank You > SHASHI
As serial output is in the time domain, you must use a timer. If you really don't want to use a clock then take your circuit diagram, remove the word "clock" and replace it with the words "timer/counter". Peter --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.659 / Virus Database: 423 - Release Date: 15/04/04
Reply by paris April 22, 20042004-04-22
"Shashi" <shashi22k@rediffmail.com> escribi&#4294967295; en el mensaje
news:7cdabebf.0404211144.38da229c@posting.google.com...
> Hi, > I'm doing a project in clockless uart..as u know that the primary > function of uart is parallel to serial conversion while transmitting > and serial to paralel conversion while receiving..I was wondering if > someone could tell me as how can i do a parallel to serial conversion > and vice versa without using a clock. > > Note: This is a circuit whoch doesnt use a clock at all/ Asynchronous > Circuit/Clockless Circuit. > > Thank You > SHASHI
and how are you planing to "sample" the input bits without a clock?, if you already figured out that part, then i guess you could use some sort of state machine ("clocked" or controled by the same circuit that sampled the bits) to deserialise those sampled bits. what kind of UART is it anyway?, and what kind of coding uses? does it use a selfclocking code scheme?
Reply by Al Kossow April 21, 20042004-04-21
> I was wondering if > > someone could tell me as how can i do a parallel to serial conversion > > and vice versa without using a clock. > > > > Note: This is a circuit whoch doesnt use a clock at all/ Asynchronous > > Circuit/Clockless Circuit. >
Use a tapped delay line. Inject a pulse to start, then time everything downstream off the taps. Loop the pulse back as necessary to extend the delay.
Reply by Jim Stewart April 21, 20042004-04-21
Shashi wrote:
> Hi, > I'm doing a project in clockless uart..as u know that the primary > function of uart is parallel to serial conversion while transmitting > and serial to paralel conversion while receiving..I was wondering if > someone could tell me as how can i do a parallel to serial conversion > and vice versa without using a clock. > > Note: This is a circuit whoch doesnt use a clock at all/ Asynchronous > Circuit/Clockless Circuit.
You could do it with a string of one-shots, but I feel guilty just suggesting such a grotesque kludge. I just put my finger down my throat and now I feel much better.