How to transfer 2MHz parallel data over 12feet

[techie]

I need to interface 6 boards to a PC which get fast data (8-bit data & 2 control lines) at about 2MHz. The problem is distance of 12 feet. I have tried using ribbon cable with TTL drivers but the signal gets too much cross talk from adjascent channels. ANy ideas what should I do.

 

[mr_ghz]

Hi techie,

you can serialize the data and transfer it with LVDS or over a coax cable.
The resulting 20MBit/s is no problem. But you have a hardware to build
on both sides...

Bye

 

[techie]

The problem is that the 12feet is not 1 length. There are 6 units connected over a bus spaced 2feet apart from each other. Making LVDS interface at each station ( 1 transmitter and 6 receivers) is expensive.

 

[elcielo]

RS-485 or ECL(LVPECL)

Maybe Low cost....

 

[dpsman]

Maybe you can use a low distributed capacity UTP or FTP cable and run each line with its own ground (the twisted one). Apart from that, you should reduce dv/dt with one pole passive filter or pi filter (like the ones used for EMI reduction on data lines but with nerarer poles ) on each data line.
In 12 feet, sure you are going to get some common mode noise, that can be reduced making a small loop inside a ferrite toroid.
It is no so expensive to try those solutions, If it doesn't work, I agree with Elcielo's solution.

 

[techie]

I was thinking of putting TTL buffers (74LS245) after every 3 feet or so. This way, 3 simple TTL buffers will make the entire lenght as 12ft without the need of any elaborate level convertors.

 

[jodokus]

I agree with the others that the best thing is to serialize the bus. Parallel data at 2msps over 12 feet is not a good idea. You can try buffers but I am afraid that differences in delay time will corrupt the data, especially when using multiple buffers in the traject.

 

[Aoxomox]

Well transfering at a datarate of 2MByte/s is not so fast. Consider Harddisks in PC with UDMA100 can transfer (ok 16bit instead of 8) 100MByte through a flat cable. If you have trouble with crosstalk put between each dataline and the next dataline a ground one. these grounds have to be conneted together on the driver side (in your case the PC). To avoid impedance missmatches put series resistor between your driver outputs and the begining of your transmission line. This will reduce the rising times of your signals. In SCSI Systems not only an impedance match at the beginning of the cable is performed but also a termination at the end. Try using 100 ohms in series at the beginning of your transmission line. I would suggest an AC Termination at the end of the line. Like 100 Ohms in series with a capacitor to ground for each signal line. You can drop the caps but the you have a voltage divider and only half of your supply voltage at your receivers.

for termination techniques look here
**broken link removed**


hope it helps,

aOxOmOx