RS232 Voltage Levels
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From: Charles Jean on 5 Jan 2006 18:09 I've got a datasheet for a chip that takes an RS232 serial input with a protocol of 9600,N,8,1. It indicates the voltage level at this input is hardware-selectable to either +/- 12V(as found from a PC serial port), and either normal or inverted TTL level(0-5V). I plan on feeding this chip a TTL level serial stream by bit-banging it rather than using a UART. 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 2)"inverted" TTL RS232 voltage levels TIA Charlie
From: Grant Edwards on 5 Jan 2006 18:41 On 2006-01-05, Charles Jean <alchemcj(a)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? -- Grant Edwards grante Yow! Yow! at visi.com
From: Charles Jean on 5 Jan 2006 19:46 On Thu, 05 Jan 2006 23:41:28 -0000, Grant Edwards <grante(a)visi.com> wrote: >On 2006-01-05, Charles Jean <alchemcj(a)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? ___ 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? Any need for a delay prior to sending the next character"? |------<--8 character bits---->-------------- +5V_|___ ___ ___ ______ | |S | | | | | | | | | | | | |T | | | | |2 STOP | |A | | | | |BITS +?V-|--|R-|--|--------------|--|--|-------------- | |T | | | | | | | | | | | |INDETERMINATE | |B | | | | |VOLTAGE | |I | | | | |REGION | |T | | | | | +?V-|--|--|--|--------------|--|--|-------------- | | | | | | | | | | | | | | | | | | | | | | | | | | | | 0V_| |__| |--|--|--|--|--| |__| | | 0 1 0 0 0 0 0 1 0 1 1 LSB MSB Bit width = 1/9600 seconds = 104.2 microseconds "Sic hoc legere scis nimium eruditionis habes." (If you can read this, you're overeducated.)
From: Grant Edwards on 5 Jan 2006 20:17 On 2006-01-06, Charles Jean <alchemcj(a)earthlink.net> wrote: >>> 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? > ___ > > Thanks Mark, for clearing that up. Who's Mark? > 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? You'll have to look at the electrical specs for the UART in question. For standard TTL, a "0" has to be below 0.7V and a "1" has to be above something like 2V. For CMOS, it's usually 1/3 and 2/3 of the supply voltage. > Any need for a delay prior to sending the next character"? Not usually, no. > > |------<--8 character bits---->-------------- > +5V_|___ ___ ___ ______ > | |S | | | | | | | | | | | > | |T | | | | |2 STOP > | |A | | | | |BITS > +?V-|--|R-|--|--------------|--|--|-------------- > | |T | | | | | > | | | | | | |INDETERMINATE > | |B | | | | |VOLTAGE > | |I | | | | |REGION > | |T | | | | | > +?V-|--|--|--|--------------|--|--|-------------- > | | | | | | | > | | | | | | | > | | | | | | | > | | | | | | | > 0V_| |__| |--|--|--|--|--| |__| | | > 0 1 0 0 0 0 0 1 0 1 1 > LSB MSB It looks like a 0x41 to me. -- Grant Edwards grante Yow! .. I at feel... JUGULAR... visi.com
From: techie_alison on 5 Jan 2006 21:47
"Grant Edwards" <grante(a)visi.com> wrote in message news:11rrh9c2vse2h8d(a)corp.supernews.com... > On 2006-01-06, Charles Jean <alchemcj(a)earthlink.net> wrote: > > Who's Mark? > Must be a spurious random message being generated by those TTL RS232 signals. Hi Charlie, have a look at the MAX232 or MAX233 (no caps). The only thing that springs to mind from reading your post is, "What on earth does this mysterious chip do, what is it called, who makes it?" |