Even if "just a few inches" you have both ends to worry about.
If does not leave the box why RS232 for "just a few inches" just put bus driver and receiver. Even simple picogate dedicated TTL inverter would do the job for short distance.
If leave the box it may not be just the driver, but shitty cable or poor receiver, or both of those and transmitter. For each signal run both ways.
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Paul Carpenter | paul@pcserviceselectronics.co.uk
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We use a PNP (BC807), emitter to +5, collector to -5v via 4k7 and to output via 100 ohms. Base - emitter resistor of 3k3, drive from processor via 10k. Handles 3v3 processors OK and runs in excess of
115200 over 5 metres. Receiver is an NPN (BC817).
If you cannot change other end, which transmits +/-9-12V levels make sure yout receiver can cope.
Another thing that has caught some people out, is check the connectors. I have seen a few applications caught out by the use of Filtered D types for EMC, limit the bandwidth or add strange loads to signals.
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Paul Carpenter | paul@pcserviceselectronics.co.uk
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On a sunny day (Sun, 11 Dec 2011 00:54:52 -0800 (PST)) it happened Rocky wrote in :
I have been using this:
Its gets it power from the DTR and RTS lines, the communication software needs to set those to + and -. also you need 2 extra wires....
Works OK at medium speed over a few meters, have not tried 115200 or higher.
On a sunny day (Sat, 10 Dec 2011 20:06:51 -0600) it happened Vladimir Vassilevsky wrote in :
Beware of latchup if you plug an external source into a CMOS gate! Not a good solution.
What an incredible problem. Add two resistors and BAV99 to protect the input and one more resistor to protect the output. Done that 1000 times, works fine for tabletop distances except for the rare case of "cable disconnect" sensitive devices.
Vladimir Vassilevsky DSP and Mixed Signal Design Consultant
good point about the filtered dsubs, it has got to be something like that I don't remember seeing much problem running 921kbit rs232, other than windows having trouble keeping up
-Lasse
On a sunny day (Sun, 11 Dec 2011 11:26:22 -0600) it happened Vladimir Vassilevsky wrote in :
It is npt a problem if you do that, but you left it out. Many peopla read this, and could get the wrong idea.
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.
The big advantage is you don't need to slew as much voltage, so it is easier to run a CMOS gate faster.
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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.
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.
external power rails wouldn't really fit without changing layouts
TI has several 1Mbit trancievers in soic16 max3232 pinout
-Lasse
So, IF you can get them, just clip off 2 pins and nobody will be the wiser..
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But no TSSOP in 18 pins. Only TSSOP 20. They really make it difficult to go high speed.
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
Tell them what they need is a fiber optics rs232
haha, blue wires. Is there some corporate talk name for these that anybody has heard?
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