Sending Serial Data from FPGA through Ribbon Cable

[fazan83]

high speed spi ribbon

Guys
Is it possible the serial data from the FPGA to the other IC or gate can be loss if we use such a long (1.5Meter) 20AWG ribbon cable?

Please advise.

Thanks in advance.

 

[sachingorkhe]

fpga serial data send

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

 

[fazan83]

ribbon cable 28awg data

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

It is a serial data from FPGA that contain Hsync and Vsync of RGB signal also contain clock signal to drive the constant current IC and ETC.
Let say the fastest speed of this signal is around60Hz.
This signal will be sent to a display.

If i plug the connection directly then there is no problem but if I use the ribbon cabble the the display will light up but in such a garbage display.
I had check the connection is correct and the current is not an issue.

I just use typical ribbon cabble almost same as the IDE cabble.

Does this problem have any issue with noise or EMI?

 

[echo47]

digital signals over ribbon cable

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]

60mhz signal ribbon cable

why not to use SDI?

 

[fazan83]

ribbon cable max frequency

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?

I see...it will try this....IC and ETC is constant current IC, multiplexer and buffers.
Yup it is a flat ribbon cable. Sorry I had checked again maximum signal speed is 30Mhz. But if I make the cabble shorter then will it help?

I need this ribbon cabble because I need to arrange a test fixture for these board.

Added after 12 minutes:

why not to use SDI?

Do you mean serial data interface?
You mean I need to modified the design for sending the signal by adding the SDI?

Also there is a lot of signal need to be sent. Total 80 pin needed if using connector.

I only want to make a test fixture for this board and try to use the simplest way for making this test fixture.

But if you have any suggestion on this please advise.

 

[echo47]

spi problems with long ribbon cable

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, avoid using 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.

 

[fazan83]

tutorial ide ribbon clock

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.

Thanks very much for your advise I will work again to fix this.
ALso need your advise.
I never use digital probe. Currently I am using agilent 3000 series that have an option for digital probe/signal.

What is advantage of using the digital signal function instead of analog signal for this oscilloscope?
Currently even examine the digital signal I am still using the analog signal funtion.

Please advise as I am really beginner in this field.

 

[echo47]

how is data sent over a ribbon cable

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?

 

[fazan83]

characteristic impedance ribbon cable ide

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?

Usually what I do is just comparing the good boards which signal all ok with boards that have the signal problem.

Does you mean that there is no great advantage if we are using the digital signal measurement function? Or in this case it will not work as we want to look the distortion that affect the signal.

Please advise.

Also for your info the digital signal probe enable us to measure up to 15 signals.
I also notice that the scope has low pass high pass filtering function even if we use the analog measurement function.
I am asking this as I am curious to know about this and for extra knowledge as I am new in this field. Hope my question is not funny.

Thanks.

 

[echo47]

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.

 

[fazan83]

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.

Understood.
Thanks again for your time to answer my doubt.