Hi,
I have a Lantronix Xport Direct + and an SSC-32. The SSC-32 runs on TTL and the XPort on CMOS. Is this an issue or will they interface correctly as is?
Cheers,
The real question is, are they both 5vdc? If so then you are good to go. 
The Xport runs on a 3.3V power supply. and the SSC-32 runs on a 6V power supply. So I guess this is an issue.
Well there is a 5vdc regulator on the SSC-32, so it’s really a 5vdc device. You will need to look into a 3.3vdc / 5vdc conversion circuit.
OK, thats what i was worried about.
Im thinking something like this will do the trick.
standardics.nxp.com/products/lvc/datasheet/74lvc4245a.pdf
That resister idea might work as well.
Cheers,
You may get out easy. Some 5v TTL gizmos may directly detect the 3.3v output of your 3.3v cmos (I think I’ve seen ~2v as the low dropout point for some 5v TTL gizmos). For your 5v gizmo to talk directly to the 3.3v cmos, you might try two signal diodes in series to drop the 5v down to 3.4v (both using a common ground). Beyond that, similar circuits to the rs232 ones below (but without the level inversion) might could be used.
Um you guys sort of jumped the gun here.
A quick review of the X-Port Direct+ Product Brief says on page 2 under Features | Serial Interface that the CMOS interface is 5V tolerant… which means that even though it is a 3.3V device the inputs are designed to accept signals from a 5V powered circuit without issue.
I would suggest you follow this up with a further review of the actual data sheet and make certain that input and output low and high voltages meet TTL thresholds. Just because the inputs are designed to withstand 5V signals does not automatically mean they will meet TTL logic thresholds, typically < 0.8V and > 2.0V. 
Ok,
If you look at page 15 in this document for the xport it says that voltage in high range is 2.0 - 5.5 V and the Voltage in low range is 0 - 0.8V.
Then from this document , which I’m not sure if I’m reading right, it kinda looks like ttl has a high range of 2 - 3.3V and a low range of
0.35-0.8V. This fits within the limits above, so I’m thinking I should be alright to just plug the Xport right into the SSC-32.
If it turns out it doesn’t work the whole things isn’t going to die is it? It just wont work right? I’m not going to fry my boards am I?
Not going to try until I’m sure it wont wreck anything.
Thanks for the help so far guys.
Cheers,
Cad you found what you needed to find so let me help you interpret it.
For TTL the max output voltage for a LOW is usually 0.4V so that it will not exceed the max input LOW threshold of 0.8V. Similarly the min output voltage for a HIGH is 2.4V and the input HIGH threshold is 2.0V. The data in the table you found indicates the device meets all of those criteria and is therefore has TTL compatible thresholds.
True CMOS thresholds are usually expressed as a percentage of the supply voltage. The problems you run into are most often that a TTL output HIGH will not meet the CMOS input HIGH threshold voltage (too low), and a CMOS output LOW will not meet the TTL input LOW threshold (too high).
Because the input voltage range is specified all the way up to 5.5V the inputs are said to be 5V compatible. If they were not then the input HIGH voltage would most likely only be specified at 3.6V to maybe as much as 4V and you would need to add something to protect those inputs from a TTL HIGH output voltage which could be as much as the TTL supply rail (5V nominal +/- 10%).
This looks like you will be just fine connecting the SSC-32 serial port lines to the Xport Direct with no risk of damage and they should work as expected.
Ahhh, Great. Thanks allot guys. Ive never dealt with logic level data before so this is all new to me. Its always fun to learn new things.
Thanks again.
Ok well I wired everything up today and I cant get the SSC-32 to run properly. I wired the TX and RX pins on the Xport to the SSC-32 using the TTL pins on the SSC-32.
I can send data to the SSC-32 and the status light will turn of when I send the first command and it will blink with subsequent commands but it will not do anything. I’ve tried to send simple servo positions as well as try to get a reading of the VA pins and i get no responce with that either. I tried running the SSC-32 right off a DB9 cable directly to my com port and it worked fine.
Any ides guys.
Cheers,
Why are you connecting to the TTL inputs on the ssc-32 instead of the rs232 tx/rx connection points?
I’m connecting it the way the manual for the SSC-32 says it should be with a bot board. So I removed the jumpers and connected the rx and tx from he Xport to the pins the way a bot board would be connected.
Thats how I though you should do it. Or should i connect them right to the DB9 port terminals?
Cad you have it correct and the xport serial should be connected to the ttl inputs of the ssc-32 just as a bot board. Zoom please read back a few post so you understand what he is connecting please. The connections to an xport are 3.3v TTL w/5V tolerant inputs, not rs-232 level signals.
Cad you might want to try the obvious and connect tx to rx on the xport and test it as a loop back with lynxterm or hyperterm. that will tell you if there is a handshake setting set to hardware rather than software or none somewhere.
Honestly though the problem sounds like it might be baud rates not matched up. I recall something in the wiport setup, which I don’t suspect is a lot different from the xport sans the wireless part, that all the baud rates had to be the same and there were like 2 or 3 places you can set it between the module and the redirector.
There is a lot of missing info to know just what the xport setup is. I assumed that the setup was rs232 > xport > ethernet > xport > rs232 (don’t understand its function otherwise). I also assume that the output from the xport is at ~TTL voltage levels (which seemed to be the origional concern), but I expect that the output of the xport is an rs232 style, ie. inverted from the usual output of a typical TTL gizmo.
um, looking at the data sheets we both linked to should resolve any questions about the output levels on the xport.
Swoosh!
Ok, I got it working. The issue was that when I used the web configuration on the Xport I changed the the baud to 12500 and clicked the done button. I didn’t realize you had to click the apply settings button on the left as well.
It works fine now.
Thanks allot guys for helping me out.
You can see what my program does here. I’m still working on the graphics glitching.
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