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High speed (230K) RS232 drivers?

Started by linnix December 10, 2011
On 12/10/2011 6:06 PM, Vladimir Vassilevsky wrote:
> > > linnix wrote: > >> We don't need a long run. It can be very short, just a few inches. > > Use general purpose CMOS inverters as drivers. All modern RS-232 ICs > have threshold at about +1.5V, so they work fine with CMOS levels. The > only problem could be some transceivers detecting low input as "cable > disconnected" condition and falling into sleep mode. > > Vladimir Vassilevsky > DSP and Mixed Signal Design Consultant > http://www.abvolt.com
The big advantage is you don't need to slew as much voltage, so it is easier to run a CMOS gate faster.
On Dec 11, 3:18=A0pm, miso <m...@sushi.com> wrote:
> On 12/10/2011 5:36 PM, linnix wrote: > > > > > > > > > > > On Dec 10, 4:43 pm, linnix<m...@linnix.info-for.us> =A0wrote: > >> On Dec 10, 3:51 pm, miso<m...@sushi.com> =A0wrote: > > >>>> For a huge length of connection you should recommend an optical link=
.
> >>>> There are (or at least were) cheap RS232 to optical converters. > > >>> Note that 232 isn't set up to handle ground offsets that are likely t=
o
> >>> occur over long distances. Optical is a great way to get around that > >>> problem. > > >>> Also there will be some asymmetry in rising and falling slew. > > >>> Back on the subject of high speed 232, these devices with charge pump=
s
> >>> on-board have jitter. Charge pumps create a lot of noise, and no amou=
nt
> >>> of bypass can filter the substrate noise. > > >>> I don't know if anyone specs the jitter, but it is easily measurable. > >>> There are internal limits on the jitter since ATE needs to know when =
to
> >>> stop looking for a transition, but the limits are huge. Doing quick > >>> tests with a storage scope, you could hit the microsecond window > >>> rapidly. Ian communication, you are sending bits forever, so someday =
you
> >>> will hit the perfect storm of jitter. Maybe 3uS for worst case margin=
.
> >>> Now you can see how using a charge pump based 232 isn't all that robu=
st
> >>> for high speed 232. > > >> So, would it help with bigger caps? =A0Are there alternative to charge > >> pumps? > > > Well, you did say the noise is internal to the chip. =A0If that's the > > case, we might have to try chips w/o pumps and w external dc-dc > > converters. > > Certainly using an external DC/DC will help. However, I don't know if > the old metal gate parts will work at high speed. > > You can measure the jitter easily with a storage scope or DSO. Test > transmitter and receiver. Drive the transmitter input from a generator. > Trigger off the generator. Store samples of the transmitter output. You > will get a fat band at the edges due to jitter. You can either drive a > receiver with the transmitter output or signal generator. Just make sure > you are triggered on the receiver input. Look for fat traces on the > receiver output. > > I assume with your own DCDC, you can use 1488 and 1489. But I don't know > if they run at high speed either. You'd have to look that up.
I did. They also max out at 115K. Linear tech has some chip for 230K, but nothing compatible with MAX232 or as small as a TSSOP 16. Perhaps someone should build a MAX232 clone using external power rails.
On 12/11/2011 5:28 PM, linnix wrote:
> Perhaps someone should build a MAX232 clone using external power > rails.
That would kind of miss the point in calling it (MAX)/(RS)232. don
On Dec 11, 4:33=A0pm, hamilton <hamil...@nothere.com> wrote:
> On 12/11/2011 5:28 PM, linnix wrote: > > > Perhaps someone should build a MAX232 clone using external power > > rails. > > That would kind of miss the point in calling it (MAX)/(RS)232. > > don
Doesn't matter what they call it. As long as it's easy to mod without changing layouts. Most of the high speed chips are too big and incompatible.
On 12 Dec., 01:38, linnix <m...@linnix.info-for.us> wrote:
> On Dec 11, 4:33=A0pm, hamilton <hamil...@nothere.com> wrote: > > > On 12/11/2011 5:28 PM, linnix wrote: > > > > Perhaps someone should build a MAX232 clone using external power > > > rails. > > > That would kind of miss the point in calling it (MAX)/(RS)232. > > > don > > Doesn't matter what they call it. =A0As long as it's easy to mod without > changing layouts. =A0Most of the high speed chips are too big and > incompatible.
external power rails wouldn't really fit without changing layouts TI has several 1Mbit trancievers in soic16 max3232 pinout -Lasse
linnix wrote:
> On Dec 10, 9:00 am, "TTman" <pcw1....@ntlworld.com> wrote: >> "linnix" <m...@linnix.info-for.us> wrote in message >> >> news:ed841358-5bde-4a55-a9bf-372aa57eda19@f11g2000yql.googlegroups.com... >> >>> Gee Wee, the customer is not happy with 115K. We already determined >>> that TI's MAX232 works up to 115K and the MAX3232 won't even work at >>> 115K (although it claims to work). I know there are pin-incompatible >>> MAX-something, but we don't want to change layout, just for the sake >>> of in-compatibility. Are there pin-compatible, reliable MAX232 clones >>> for 230K that work, not just claim to work? Thanks. >> Max 3222 ? > > 18 pins vs. 16 pins
So, IF you can get them, just clip off 2 pins and nobody will be the wiser..
On Dec 11, 10:03=A0pm, Robert Baer <robertb...@localnet.com> wrote:
> linnix wrote: > > On Dec 10, 9:00 am, "TTman" <pcw1....@ntlworld.com> wrote: > >> "linnix" <m...@linnix.info-for.us> wrote in message > > >>news:ed841358-5bde-4a55-a9bf-372aa57eda19@f11g2000yql.googlegroups.com.=
..
> > >>> Gee Wee, the customer is not happy with 115K. =A0We already determine=
d
> >>> that TI's MAX232 works up to 115K and the MAX3232 won't even work at > >>> 115K (although it claims to work). =A0I know there are pin-incompatib=
le
> >>> MAX-something, but we don't want to change layout, just for the sake > >>> of in-compatibility. =A0Are there pin-compatible, reliable MAX232 clo=
nes
> >>> for 230K that work, not just claim to work? =A0Thanks. > >> Max 3222 ? > > > 18 pins vs. 16 pins > > =A0 =A0So, IF you can get them, just clip off 2 pins and nobody will be t=
he
> wiser..
But no TSSOP in 18 pins. Only TSSOP 20. They really make it difficult to go high speed.
On 12/12/2011 9:42 AM, linnix wrote:
> Max 3222
The MAX 3222 has the same pin out for the lower 16-pins and the MAX 232. ( they must have thought this thru) Pin 1 and 18 are *Enable and *Shutdown. So, this part can be made to work, if Blue wires don't bother you till the next board layout. Shutdown is next to Vcc and Enable is across from GND. So small wires. don
On Dec 10, 10:47=A0am, linnix <m...@linnix.info-for.us> wrote:
> Gee Wee, the customer is not happy with 115K. =A0We already determined > that TI's MAX232 works up to 115K and the MAX3232 won't even work at > 115K (although it claims to work). =A0I know there are pin-incompatible > MAX-something, but we don't want to change layout, just for the sake > of in-compatibility. =A0Are there pin-compatible, reliable MAX232 clones > for 230K that work, not just claim to work? =A0Thanks.
Tell them what they need is a fiber optics rs232
In sci.electronics.design hamilton <hamilton@nothere.com> wrote:
> On 12/12/2011 9:42 AM, linnix wrote: >> Max 3222 > > The MAX 3222 has the same pin out for the lower 16-pins and the MAX 232. > ( they must have thought this thru) > > Pin 1 and 18 are *Enable and *Shutdown. > > So, this part can be made to work, if Blue wires don't bother you till > the next board layout.
haha, blue wires. Is there some corporate talk name for these that anybody has heard?