pin states (simple matter)

so l'ets say there is an 8bit bus that is carrying data .. i want to spy on the data being transmitted . so then i need to connect 8 arduino pins to every rail of the bus , will the pins being connected to the bus , affect it in anyway ?

If voltage levels are within tolerance of the Arduino, then there would only be a very, very small loading effect similar to that of any CMOS input. Seems like it would be beneficial to monitor the signals quickly and simultaneously … look into reading a port (8-bit) in just one read.

What specifically is the 8-bit bus?

dlloyd: If voltage levels are within tolerance of the Arduino, then there would only be a very, very small loading effect similar to that of any CMOS input. Seems like it would be beneficial to monitor the signals quickly and simultaneously ... look into reading a port (8-bit) in just one read.

What specifically is the 8-bit bus?

it's an old system that has an 8bit data-bus . i want to read the binary data and also edit it . and yes the voltage levels are within the tolerance of arduino

will the pins being connected to the bus , affect it in anyway ?

Basically yes, you can not make a measurement of any kind without disturbing the system. That is a basic law of physics.

I think what you are asking is will it affect the system such that it stops working? This is possible due to increased capacitance loading caused by your input pins and the wires connecting them. A lot depends on the nature of the bus you are trying to tap, its speed and the drive capacity of the signals driving the bus.

You will probably not disturb the system enough to stop it working but you might, there is no way of telling without a detailed examination of what bus you have, or of course, trying it.

Is it a CPU databus? If so, the Arduino is too slow to capture the changes. You are essentially building a logic analyzer.

Is it a CPU databus? If so, the Arduino is too slow to capture the changes.

Depends on the speed of the bus. A lot of old systems only had a 1MHz bus.

good , thank you . now , can i edit the signal ?

amine2: . now , can i edit the signal ?

What does that mean?

I think he wants to do like hardware packet injection.

Yes…is the answer…but it depends on the system/protocol you are trying to “inject”.

But this is all I can say from the information given. Yes, an arduino can make lines high/low on a wire BUS. It can also read them.

Now, what is the data rate / bandwidth or the frequency of the port?

reading was successful as far as now , but i did not try injecting anything to the signal . due to the variation of data over time , you cannot set an exact frequency to it , but after reading data out of it for a while , the frequency does not pass 100Khz (far out approximation)

On your "bus" one side will be output, the other is input. If you "inject" you are tying two outputs together. That will result in unpredictable voltage levels unless the "injector" has a much lower impedance than the bus outputs. Then you run the risk of damaging the bus, unless you have a way to temporarily disable the outputs when you do a write ("inject") operation.

Also, is there a clock line?

amine2: so l'ets say there is an 8bit bus that is carrying data .. i want to spy on the data being transmitted . so then i need to connect 8 arduino pins to every rail of the bus , will the pins being connected to the bus , affect it in anyway ?

What voltage(s) are involved? What logic family? Is this an open-collector bus?

You didn't mention data flow control on the bus. The are usually:

Data direction Write Strobe Read Strobe There may be a Bus request and a Bus acknowledge as well if there are multiple controllers.

Like was said, what are you looking at? Dwight

so let’s say there is an 8bit bus that is carrying data … i want to spy on the data being transmitted .

That’s a rather odd way to phrase it. Normally a request would be worded:

“I would like to monitor an 8-bit data bus…”

Are you really "spying " ?
Where is this data bus ?