fazan83
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sachingorkhe said:Hi Fazan,
Plz let us know which type of serial data you want to send over ribbon cable? Is that RS232? SPI or I2C?
Sachin
Added after 31 minutes:
For RS232, standards to 256kbps or less and line lengths of 15M (50 ft) or less. But the rule of thumb for the length a data cable depends on speed of the data, quality of the cable.
For SPI, I have tested the SPI up to a distance of 15m between Master and Slave on SPI over a twisted pair cable
For I2C, The maximum bus capacitance is 400pF, which sets the maximum number of devices on the bus and the maximum line length.
In typical applications, the length is a few meters (9-12ft). The length can be increased significantly by running at a lower clock frequency. One particular application - clocked at about 500Hz - had a bus length of about 100m (300ft). If you are careful in routing your PCB's and use proper cabling (twisted pair and/or shielded cable), you can also gain some length.
Plz let me know if you have any query regarding the same.
Sachin
echo47 said:around60Hz - did you mean 60 MHz?
I assume it is flat ribbon cable, not twisted-pair. Correct?
20 AWG is much much bigger than IDE ribbon cable (28 AWG).
At 60 MHz, you need to arrange the cable's high-speed signals as ground-signal-ground-signal-ground-.., and then terminate each signal with a resistor equal to the cable's characteristic impedance, to avoid severe signal reflections. I don't know your exact cable type, but a wild guess is about 150 ohms.
What are IC and ETC?
Iouri said:why not to use SDI?
echo47 said:At 30 MHz you still need good cable design and termination, even if you significantly shorten the cable.
Examine your signals with a fast oscilloscope, and you'll see the problem. Remember, when measuring fast signals with an ordinary passive probe, don't use the probe's standard ground lead, because it has lots of inductance. Instead, use a very short connection from the probe's ground ring to your circuit board ground.
If your cable connections don't have enough room for grounds between every high-speed signal, maybe you can use a technique similar to the hard drive industry -- manufacturers switched from plain 40-conductor cables to special 80-conductors cables with grounds between every signal.
echo47 said:A beginner? Welcome!
You are troubleshooting a somewhat tall problem for a beginner.
When troubleshooting digital signal quality issues, you want to observe the signal's analog waveform to look for distortion. I don't know what a "digital probe" is, but if it converts the waveform to ones and zeros, then you don't want to use it in this situation.
I've never used an Agilent 3000 scope. If you have one of the lower bandwidth models, it may not clearly show distortion in a 30 MHz signal.
The 3000 scope provides several "digital filtering functions". That doesn't mean it's some kind of digital or logic display. It means that it uses a microprocessor to do high-pass, low-pass, and other kinds of filtering on analog waveforms. You don't need them here.
Does anyone here know a good illustrated tutorial describing how to probe digital transmission line problems?
echo47 said:You want to display the waveform as faithfully as possible, so set your scope to full bandwidth, and disable all special processing and filtering. Someday you may need to use the special processing features, but not now.
The digital probe is probably very handy for displaying a group of clean digital signals, but for troubleshooting a signal integrity problem you need to see the analog waveform.
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