Monitoring RS485

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Hi all,

i need an informatio about rs485:
I need to watch netwrok trafic from my device and another device that
use rs485  to comunicate. Is possible to connect in parallel mode
another peripherical (like a pc via rs232) to trace all the message
that is exchange from two device?

Thanks in advanced


Re: Monitoring RS485

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Use a MAX485 or similar to convert the signals to TTL RS232 and then a
MAX202 or similar to get back to true RS232.  With luck your serial port
might take the TTL levels.  The baud rates for most application are
generally the same as standard RS232 baud rates.  You might have to check
with a scope if not sure.  Then use a RS232 terminal emulator of some sort.
HyperTerminal in WinXP is one example.

Re: Monitoring RS485
I have used a home made device, along the lines of Fred's description,
to do exactly what you are asking.  The device tapped off of the rs-485
lines with a cmos inverter and then fed the inverter output to a rs232
driver.  Jumpers were used to select one or two inversions as
necessary.  using two of the devices, and a program I haven't been able
to locate (though I wish I could - it was called something along the
lines of datascope or pals), I could monitor both the recieve and
transmit channels simultaneously.

I would imagine that there are commercially available tools available
for this purpose, but I have no idea how much they would cost, but
probably  a lot.  You could probably make up your own circuit easilly
enough, but then you would still need to find a monitoring program.

Re: Monitoring RS485

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i have always used my olg greenleaf VC.EXE program to see side-by-side
output from my sniffer hardware.

greenleaf is alive and well at:


Re: Monitoring RS485
On 30 Nov 2005 06:00:12 -0800 in comp.arch.embedded, "chris"

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Comlite32 is a free tool from that lets you monitor COM
traffic in your Windoze box.  Not a terminal program, but lets you
watch the communications traffic.


Change is inevitable, progress is not.

Re: Monitoring RS485

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RS485 does not specify the protocol used. Connecting an RS-485 buffer
such as a MAX485 or similar is not a problem. (Keeping things such as
stubb lengths etc. in mind). If the protocol used is asynchronous
serial, then adding an RS-232 buffer such as a MAX232, and then
connecting this to a standard PC serial port is all that is needed.
Plus software of course.

  Anton Erasmus

Re: Monitoring RS485
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I've done similar. RS485 to RS232 converter. Used to capture RS485 data.
Used a scope to find the data rate and wrote the converter software to
simply package up the received RS485 data and send out as RS232 for logging
on a PC. You end up with lots of data but making sense of it is another
matter. I had part of the original protocol document and needed to fill in
the gaps so it was fairly easy.

If you need general RS485 info or need to purchase an RS485 to RS232
converter try . Best site on RS485 I've ever found.

Good luck

Re: Monitoring RS485
During my search for a commercial converter I found this one: ...

this is very cheaper but i'm not sure that is what i need.
Some one can see this item or know what this item do?


Re: Monitoring RS485

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This is an RS485 - RS232 signal converter. It converts the signal levels
only. That is, the differential RS485 signals are 'converted' to RS232
levels. If you can match the baud rate, number of data bits, stop bits etc.
between a PC and the RS485 comms then you should see a stream of data if
using hyperterminal.

I use devices exactly the same as these to log RS485 data on a small RS485
network. I know the protocol used though and this is essential to
understanding what's going on.


Re: Monitoring RS485
I think that's a big trouble, i don't know how this device work. I have
a keyboard connected with a device and i need to see what message are
exchanged from this two. But i see only that the two device use rs485
to comunicate. Do you think this is an impossible mission? Some help
for me?


Re: Monitoring RS485

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To help further,

1) Do you mean that the keyboard is communicating with this 'device' using
RS485 signal levels?
2) Do you know this because you have opened up the case and looked at the
driver chip?
3) Have you monitored the data using a scope?
4) What is the 'device'?
5) Do you know if data is only on the bus when a key is pressed or is data
always apparent (when no keys are pressed)?

In this area nothing is impossible. If its genuine RS485 signal levels and
uses a reasonble protocol (8 or 9 data bits, start & stop bits etc.), then
it could be very easy to capture the data.

What you do with that data is probably the hard part.  If all you need is to
see what data is sent on a keypress on the keyboard then this sounds easy...
it all depends.

It's hard not seeing the two devices and not knowing what you are after
exactly, to say easy or hard. But generally getting the data is easy.
Working out what the data does etc. is hard and sometimes VERY hard. If lots
of continuous random looking data and/or data is encrypted in some way then
I wouldn't even bother. But you won't know that unless you have a first stab
at it. Get a scope on the job first. If you can capture a burst of data from
a keypress and your scope has deep memory then you can decipher small
packets by measuring the bits (I hate doing this as it takes ages, but in
your case it would be a start)



Re: Monitoring RS485
Ok, i opened the box that contains the device, the Keybord isn't only a
keyboard but contains a display and some output device, the
comunication, I think, is full duplex.
1) The keybord is used to setting configuration parameter, the lcd
display and other led's to output the configuration and state
2) No, the driver chip isn't visible, is covered.
3) No, but this is a good idea
4) The device contains a microprocessor or microcontroller, but all the
Integrated Circuit is covered and serial number erased.
5) The data is bidirectional mode from the First device to the second
and return. My plan is to generate an output from the main device to
the keybord and display. Then press a key and see what data is
exchanged. Then i think to generate all the possible output to build
the tree of command and signal.

When I opened the main device I saw printed on board where the keyboard
is connected "RS485" with connections named "A, B , +, -". Only 4 wire.

Jim, thank you for help

Re: Monitoring RS485

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Is this a keyboard for a Point of Sale device?

Re: Monitoring RS485
No, but this isn't a quiz like "what type of device is?" :) . The
device is a central for fire alarm.

Re: Monitoring RS485
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Do you mean the main control panel device for a fire panel?. What
manufacture and model number is it? I only ask because I have a college who
used to work for a fire panel manufacturer. He might be able to shed some
light on the subject.

From your answers to my long query list it can almost be assumed that the
(lets call it an FP for now), FP microcontroller is controlling the RS485
bus. Therefore it would also be reasonable assumption that it is using a
standard UART and therefore that the data will be able to be picked out
using PC software (Although standard PC UARTS do not support 9-bit data it
is possible in most cases to use the parity bit for the 9th bit, unless the
protocol is using parity as well - lets assume that this is not the case).

My suggestion would be to get hold of one of those RS485 to RS232
converters. Hook it up to a PC serial port and connect the RS485 end to the
bus. You will not need to transmit onto the bus and so this should be quite
easy. Next, scope the waveform on the bus and determine the baud rate and
bit depth, stop bits etc. Then set these parameters in hyperminal and see
what data you capture. Unfortunately because hyperterminal is not a binary
to ASCII converter you will only see ASCII valid charaters and its possbile
that some data will be lost. Once you have this working then you need to
find/beg/borrow/write etc. an application that allows you to capture binary
data (0-255) and be able to display the digits 0-255. If you know VB or VC++
or whatever then this is quite easy using the MSCOM control and in fact if
you got to the "code project" website ( you might find
someone has already done one (not checked so I don't know if this is the

Then... start deciphering..

Good luck!

wireless ... bluetooth ?

I thinking of realizing a wireless link, from a portable PIC system to a PC.
The needed datarate is about 100 kbit.
No (or maybe very slow) data from PC to PIC.

Another requirement is to use as much standard components as possible.

So there seems 2 ways to go:  wifi  or  bluetooth.

Now my guess is that bluetooth devices are easier to interface with a pic,
and more general available (in small quantities)  then wifi.

Anyone has experience with these interfaces ?
Any other comment ?

Stef Mientki

Re: Monitoring RS485 says...
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Or just use a reasonable terminal emulator.  For Windows based PCs
Realterm come to mind but there are others.  FOr that matter it was
possible to do this with PC-Kermit if I remember correctly.  
Hyperterminal is worth rather less than you paid for it.


Re: Monitoring RS485
Well, after some day of work i have this trouble:
- I don't know what is the speed of the device
- I don't know how many bit it ues
- I don't know if parity bit is present

Then when I connect the PC with the two device, the display of second
device (the keyboard, with lcd display) send a connection error (open
the connection via Hyperterminal).
What my problem? How i can decide what is the configuration parameters
for Hyperterminal (speed, data bit number, parity, stop bit number,
ecc...)? It's linked with integrate type? I can read the IC's part
number than I can search for spech?

Thanks in advanced

Re: Monitoring RS485
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With an oscilloscope, you can tell the speed within seconds.

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If single bytes are sent with delays between, see above.

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See above.

Hyperterminal is crap. When you open a com port with data present, hyperterm
says it cannot open the port in 95% of the cases. This is a hyperterminal
error. Use for instance TeraTerm (free), which works like a charm. With TT
you can also change all com settings (baud, bits etc) on the fly without
having to close the connection first, like hyperterm wants.

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Drop hyperterm and use decent software.


Re: Monitoring RS485
What software? can you give me some one?

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