Grant Edwards wrote:> On 2006-01-05, Charles Jean <alchemcj@earthlink.net> wrote: > > >>I am familiar with the polarities and V requirements of the >>"real" RS232 as shown in the example below for ASCII 65("A"): >> >> >>+15V-|------<--8 character bits---->-------------- >> | ___ _______________ ___ >> | |S | | | | | >> | |T | | | | | >> | |A | | | | | >> +3V-|--|R-|--|--------------|--|--|-------------- >> | |T | | | | |INDETERMINATE >> | | | | | | |VOLTAGE >> 0V-|--|B-|--|--------------|--|--|-------------- >> | |I | | | | |REGION >> | |T | | | | | >> -3V-|--|--|--|--------------|--|--|-------------- >> | | | | | | | >> | | | | | | | TWO >> | | | | | | | STOP >> | | | | | | | BITS >> ____|__| |__| | | | | |__| |__|__| | | | >> | 0 1 0 0 0 0 0 1 0 1 1 >>-15V-|------LSB------------------MSB-------------- >> >>Bit width = 1/9600 seconds = 104.2 microseconds >> >> >>Can someone please educate me as to what are: >> >>1)"normal" TTL RS232 voltage levels > > > There is no such thing as "TTL RS232 voltage" levels. > > UARTs send/receive a logic "1" (e.g. 5V or 3.3V) for a mark, > and a logic "0" (e.g. 0V) for a space. > > >>2)"inverted" TTL RS232 voltage levels > > > You really don't know what it means to invert a TTL signal? >I believe a logic 1 is negative and a logic zero is positive as per the elegant diagram provided by the O.P. . For a teletype, i think (it has been a few daze) a mark was current flowing for a logic one.
RS232 Voltage Levels
Started by ●January 5, 2006
Reply by ●January 6, 20062006-01-06
Reply by ●January 6, 20062006-01-06
On Fri, 06 Jan 2006 00:46:10 GMT, Charles Jean <alchemcj@earthlink.net> wrote:>Thanks Mark, for clearing that up. Does this look like the proper way >to send the chip an "A", then, with the mode set at "normal" >TTL(0-5V)? What are the indeterminate voltage limits?How long distances do you intend to transfer the TTL signal ? Is there a cable between the devices or is this just a PCB track above a continuous ground plane ? The standard TTL maximum receiver "0" state voltage is 0.8 V, so if you have some ground potential differences, such as ground bounce due to fast peak currents or feeding both equipment from a single DC power supply with common 0 V causing large ground return currents, your "0" state noise marginal can be quite quickly ruined.>Any need for a delay prior to sending the next character"?If you are using bit banging, you usually have some degree of uncertainty about your timing. I would suggest that you on transmit generate at least 2 (or even more) stop bits and on receive, always accept a new start bit after 1 stop bit (or even 0.5-0.7) stop bit time, regardless what the specification says about the number of stop bits in each case. This ensures a reliable connection even if the sampling points are a bit off and only reduces the throughput about 10 % on transmit. Paul
Reply by ●January 6, 20062006-01-06
On Fri, 06 Jan 2006 12:21:56 +0200, Paul Keinanen <keinanen@sci.fi> Gave us:>How long distances do you intend to transfer the TTL signal ?Can you say "False low"?
Reply by ●January 6, 20062006-01-06
Paul Keinanen wrote:> Charles Jean <alchemcj@earthlink.net> wrote: >... snip ...> >> Any need for a delay prior to sending the next character"? > > If you are using bit banging, you usually have some degree of > uncertainty about your timing. I would suggest that you on > transmit generate at least 2 (or even more) stop bits and on > receive, always accept a new start bit after 1 stop bit (or even > 0.5-0.7) stop bit time, regardless what the specification says > about the number of stop bits in each case. This ensures a > reliable connection even if the sampling points are a bit off > and only reduces the throughput about 10 % on transmit.The receiver will normally sample the incoming line at 1/2 bit time from the nominal transition. Once the stop bit has been sampled, it should immediately go into a 'hunt' mode for the start bit of the next character. This automatically yields 1/2 bit of timing slop. So there is never any point to using more than two stop bits at the transmitter. -- Some informative links: news:news.announce.newusers http://www.geocities.com/nnqweb/ http://www.catb.org/~esr/faqs/smart-questions.html http://www.caliburn.nl/topposting.html http://www.netmeister.org/news/learn2quote.html
Reply by ●January 6, 20062006-01-06
On Fri, 06 Jan 2006 09:46:11 GMT, Robert Baer <robertbaer@earthlink.net> wrote: [snip]> There may still be some devices that will convert RS-232 levels to >TTL and some that go the other way.RS-232 -> TTL = MC1489 TTL -> RS-232 = MC1488 These chips are still available more than 40 years after I designed them ;-) These chips adhere to the original RS-232 spec. Later versions, such as some of those from Maxim, are "one-sided", 5V-only devices. ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●January 6, 20062006-01-06
On 2006-01-06, Robert Baer <robertbaer@earthlink.net> wrote:>>>Can someone please educate me as to what are: >>> >>>1)"normal" TTL RS232 voltage levels >> >> >> There is no such thing as "TTL RS232 voltage" levels. >> >> UARTs send/receive a logic "1" (e.g. 5V or 3.3V) for a mark, >> and a logic "0" (e.g. 0V) for a space. >> >> >>>2)"inverted" TTL RS232 voltage levels >> >> >> You really don't know what it means to invert a TTL signal? > > I believe a logic 1 is negative and a logic zero is > positiveNo. TTL didn't use any negative voltages. Logic 0 is <0.7 and logic 1 is >2.X. Inverting a TTL signal means you convert a Logic 0 to a Logic 1 and vice versa. A Boolean "not".> as per the elegant diagram provided by the O.P. . For a > teletype, i think (it has been a few daze) a mark was > current flowing for a logic one.He's asking about TTL. I think. -- Grant Edwards grante Yow! It's OKAY --- I'm an at INTELLECTUAL, too. visi.com
Reply by ●January 6, 20062006-01-06
"Jim Thompson" wrote ...> These chips are still available more than 40 years after I designed > them ;-)Do you have a "top-10" list of Thompson's Greatest Hits? I see your air freshener puffing away frequently on TV. How did they select thost (odd) intervals?
Reply by ●January 6, 20062006-01-06
On Fri, 6 Jan 2006 07:48:31 -0800, "Richard Crowley" <rcrowley@xpr7t.net> wrote:>"Jim Thompson" wrote ... >> These chips are still available more than 40 years after I designed >> them ;-) > >Do you have a "top-10" list of Thompson's Greatest Hits?MC1488/89 RS-232... still in manufacture MC1530/31 OpAmp... still in manufacture MC1650/51 HS Comparator... still in manufacture All the PLL stuff, VCO's, VCM's, phase detectors... most still in manufacture Automotive stuff in the '60's, early '70's USB driver/receiver for Intel Roughly 160 custom chips (ASIC's)... the largest source of my income ;-)> >I see your air freshener puffing away frequently on TV. >How did they select those (odd) intervals?I designed the combination flyback power supply / driver for the piezo pump, and the low power clock. Two associates of mine in Columbus, Ohio, did the "microprocessor". The odd intervals probably came from how rudimentary the uP is. ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●January 6, 20062006-01-06
Robert Baer <robertbaer@earthlink.net> writes:> There is no such thing as a TTL RS232 level; there are the nominal > TTL levels (0 to 0.8V for a low or "zero" and 2.4V to 5.0V for a high or > a "one"), and there are the levels for RS-232 which you have so > elegantly demonstrated. > There may still be some devices that will convert RS-232 levels to > TTL and some that go the other way.EIA RS232 spec says that the max. voltage level is 15V. It also says that the minimum non-space voltage level is (7.5V?), but most devices will work at lower levels so TTL signal levels work but not be in conformance with the standard.
Reply by ●January 6, 20062006-01-06
On Fri, 06 Jan 2006 07:35:49 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@My-Web-Site.com> wrote:>On Fri, 06 Jan 2006 09:46:11 GMT, Robert Baer ><robertbaer@earthlink.net> wrote: > >[snip] > >> There may still be some devices that will convert RS-232 levels to >>TTL and some that go the other way. > >RS-232 -> TTL = MC1489 > >TTL -> RS-232 = MC1488 > >These chips are still available more than 40 years after I designed >them ;-) > >These chips adhere to the original RS-232 spec. ><snip>1488 requiring several supplies -- and runs hot as a pistol, too. I've got a box of both; they were about all there was to use in the market and worked well when I was using them; but don't use them much now because of the power requirements (especially the 1488) and the serious heat to be removed (again the 1488 much more than the 1489, if memory serves, but neither of them slouches in the heating department.) Jon
