unknown serial protocol - (RS-232. 422 pLAN ) ??

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- Darragh
  
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posted
15 years ago

Sat, Feb 7, 2009 9:18 PM

Hi, I'm currently trying to interface 3 Air Coolers to a remote monitoring system, over a serial link, but after looking into it further, the Controller has a strange serial interface, (see pic) what looks like a RS-232 has strange labels, from what i can tell is, the 3 coolers are networked to each other, and if an alarm goes off the other cooler will kick-in.

It looks like a RS-232 or something similar, however RX-TX- are assigned to a single pin! also RX+TX+, in the image it shows the 3 pin connector call pLAN, GND, RX- TX-. RX+ TX+,

formatting link

I'm hoping to be able to reverse engineer the protocol that communicates between the coolers so that when an event happens I'll be able to tell if the cooler is down or not

If anyone has done something similar please let me know

Many Thanks in Regard Darragh

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posted
15 years ago

Sat, Feb 7, 2009 9:45 PM

Half duplex RS485 at a guess.

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posted
15 years ago

Sat, Feb 7, 2009 9:46 PM

..... can you trace the tracks back to a line driver?

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Regards,
Richard.

+ http://www.FreeRTOS.org
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+ http://www.SafeRTOS.com
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- Darragh
  
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posted
15 years ago

Sat, Feb 7, 2009 10:41 PM

.

I tried to, and looked for a MAX232 IC but no luck, they go back into the Micro above the connector, my guess I2C, giving that the cable is daisy-chained to each of the coolers

any guess on how i maybe able to sniff the data out of it?

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- drn
  
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posted
15 years ago

Sat, Feb 7, 2009 11:22 PM

...

at

X+

Yup, looks like RS-485. Try using up a MAX1483 in receive mode... Hope that helps, Best Regards, Dave

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- vorange
  
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posted
15 years ago

Sun, Feb 8, 2009 12:14 AM

maybe this ?

formatting link

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- Darragh
  
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posted
15 years ago

Sun, Feb 8, 2009 12:53 AM

om...

what

,

RX+

Cool Guys! really quick replay! It's looking more like a RS-485 I'll do up a RS-232 circuit to RS-485 and get it connected to a pc, that said, it's been a while since i've done some electronics, any new apps out their to detect BAUD rate, party, stop bit, etc..

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- rickman
  
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posted
15 years ago

Sun, Feb 8, 2009 1:17 AM

...

at

X+

I see the connector, but I can't trace the pc connections. If you say it goes to the MCU, I'll take your word for it.

RS-485 is spec'd as a 5 volt differential interface with tri-stated driver outputs. This allows the two wires to function as both tx and rx. If you want to "sniff" it, you can just look at the TX+/RX+ signal. You will likely see it at +5 volts normally and brought low when a transmission is made. With a scope you can figure out the baud rate and the configuration (parity, data bits, stop bits). To monitor the line, you can drive an RS-232 driver with this signal and then to a PC.

Rick

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- Tim Wescott
  
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posted
15 years ago

Sun, Feb 8, 2009 2:48 AM

snipped-for-privacy@m40g2000yqh.googlegroups.com...

Not all driver chips are MAX232 -- find out what's driving those lines, and you're a long way to finding out what the physical layer is, if not the protocol.

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- Falk Willberg
  
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posted
15 years ago

Sun, Feb 8, 2009 8:45 AM

Darragh schrieb: ...

A scope.

Falk

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- Paul E. Bennett
  
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posted
15 years ago

Sun, Feb 8, 2009 10:14 AM

[%X]

As someone already suggested it looks like RS485 would be a good guess to start with. Try hooking in an RS485 converter to your PC and scope between the lines with a differential probe to see what the traces look like as you try to elicit activity from it (ENQ is always a good first prompt character to try). This way you may discover the baud-rate and what the device is sending in response to your prompting. Once you begin to have a dialogue things should become clearer.

Alternatively, can you not find the manufacturer of the coller board and just ask them for the protocol details?

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- Rich Webb
  
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posted
15 years ago

Sun, Feb 8, 2009 2:34 PM

Note to the OP that the RS-422 & -485 "A" side is mark (idle state) low with respect to the "B" side. It's not at all uncommon for the labels to be reversed so it may be worth flipping the connections if the PC reports gibberish.

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Rich Webb     Norfolk, VA