TTL voltage on RX line

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Hello all,

 

I am working with a device which has a TTL UART interface. I want to check which lines correspond to the TX and RX on this device. The device has a 5-pin connector, So far I have checked the voltage levels on these pins and they are as follows:

 

PIN1 -> +12v

PIN2 -> +0.8v

PIN3 -> +5.7v

PIN4 -> +0.8v

PIN5 -> +5v

 

From my understanding, I think that the pin with +5v is the TX pin since the idle TTL UART voltage level is +5v. I am not sure about the RX line and from what I understand it could be any one of the +0.8v lines. I would appreciate if someone could confirm this.

 

Thanks.

Best regards,

Owais.

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Link to your device or datasheet??

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Thanks for your response. I have the device datasheet but it does not indicate the pinout for the connector I mentioned above. I have attached the device datasheet link as follows in any case:

 

http://www.konvekta.de/fileadmin/Service/Haendler_intern/Serviceportal/Transport/Infos/Steuerung/FR4.1/11002347_2AA-a00_Instructions_for_installation_and_service.pdf

 

The connector is used for the purpose of servicing and for that reason I believe the connector pin out is not mentioned in the datasheet.

 

Thanks.

 

Best regards,

Owais.

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Based on the voltage levels you measured, it is not clear which pins are Tx or Rx.

Note there is no 0V on that connector. What did you use as ground reference ?

 

See if you can open the housing.

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If you look at section 9.1 on page 13 of the data sheet you linked to, you will find there are no connections to RX or TX signals. It appears to be a strictly stand alone temperature controller.

Last Edited: Wed. Jun 29, 2016 - 12:27 PM
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I saw that too, but apparently OP is referring to a different connector.

 

Nard

 

Edit:

Took an even closer look. SG, see page 11, the picture. Do you spot the 5 pins connector on the side of the unit ? Picture on the right.

 

To OP: there may be an optocoupler between the 5 pins service connector and the processor. Or some transistor configuration.

It looks German and industrial. Pretty sure they put some protection circuitry in. And not to lock you out, but just for safety.

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

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Last Edited: Wed. Jun 29, 2016 - 12:59 PM
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there are no connections to RX or TX signals

He's referring to the 5-pin "Copy Key" connector.  Ditto Plons' question: what did you use as a reference when you measured the voltage?

Greg Muth

Portland, OR, US

Xplained/Pro/Mini Boards mostly

 

Make Xmega Great Again!

 

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@Plon & @Greg: I used a lab power supply to power up the device with +12v and used the negative terminal of the supply as the reference for measuring the voltage. 

Best regards,

Owais.

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In the meantime I edited my post. Have a look :)

 

Edit (again!):

Osyed, you said in your OP     I am working with a device which has a TTL UART interface.

Understandable assumption but no, not very likely to be just that.

 

Like I said earlier: it looks like an industrial controller. Can you open it ?

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

Last Edited: Wed. Jun 29, 2016 - 01:09 PM
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I'm not "yet" convinced it is a uart interface, it could be a form of SPI???

 

 

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@ki0bk: Possible, not likely. It is German.

 

To Owais: if you put a 10k resistor across the terminals of your multimeter, and measure again .... what are the readings then ?

(Although opening the housing is IMO a much better approach)

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

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The fact that there is no 0V on the service connector, makes it unlikely to be plain logic level.

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Have you tried using the email address or other contact info given in that document?

Top Tips:

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@Plons: Since the device belongs to a customer therefore I was a bit reluctant to open it at first but now I have the permission to open it and study further. I am now tracing all the pins on this connector, any suggestions?

Best regards,

Owais.

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Post a picture laugh

As a starter.

 

Disconnect all power connections

Use a multimeter in low Ohm range.

 

Start at a pin of the service connector, use eyes and flashlight to follow the tracks and the first IC or transistor gives the first clue.

(re-thinking the levels .... it could be RS485 .....)

 

Reverse engineering is an art: it requires talent but with dedication you'll get there too.

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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First of all, determine if the device is using RS232 voltage levels for its UART interface that plugs into the connector.   Before USB, computers and serial peripherals that used UARTs would have minus 9v to minus 12 volts be the signal for the TX and RX lines at rest.  That is ready to receive or transmit.  This minus voltage corresponds to the +5V coming out of the UART TX pin when there is no data being sent.  Serial data would pull the TX line low to ground at the UART, but the RS232 voltage level for this state would be +9 to +12 V.

 

If your device is pre-USB, say before 2008, then it is likely to use these voltage levels for serial interfacing.  Plus a ground shared between the PC , or embedded microcontrollerand the device.

 

First, find the ground on your 5-pin connector. Test for continuity between your meter's ground and the 0.8 v pins (with the power off).

The +12 volts is likely to be a power source instead of an RS232 signal, because the RS232 non-active voltage (call "SPACE" if I recall) is negative.

 

Next send some data out and see which pins change their levels with an oscilloscope.

 

Contact the people who made the machine that the 5-pin plug is coming out of. Maybe they have schematics and data.

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Thanks all for your valuable time and comments. I received information from the provider that this port is only fro service purpose and is not to be used by the end user. However I have managed to get in contact with the technical department and they are willing to assist me further in this regard.

 

Once again thanks for all the troubleshooting suggestions.

Best regards,

Owais.