sn65hvd78 data transmission problem

mahmut turk

Other Parts Discussed in Thread: SN65HVD78

Hello all,

In my project, i use sn65hvd78 rs485 tranciever to transmit and receive 15mhz clock and data signals. I use one sn65hvd78 to transmit and one for receive. I use a 5 meter CAT5 cable. The problem is that sometimes the data comes deformed. I wonder the reason of it. I use a 100 ohm resistor between A and B nodes in receiver side. I used no more components such as capacitors. I also wonder if there is more efficient way of sending high frequency data and clock signals far away.

Thank you,

over 11 years ago

0 Thomas Kugelstadt over 11 years ago

TI__Mastermind 28265 points

Please, what do you mean with "data comes deformed"? Do you measure at the receiver input ? How do you measure the differential signals ? Typically you should measure the A-signal with respect to ground and the B-signal with respect to ground and then perform the Math-function with the oscilloscope.

Could you please provide some sope pictures and a schematic?

Since the distance is 5m only, could you measure the difference between the ground of the driving transceiver and the ground of the receiving transceiver?

Thank you, Thomas

0 mahmut turk over 11 years ago in reply to Thomas Kugelstadt

Intellectual 300 points

hello Thomas,

what i mean by saying deformed is that sometimes the recived data at the receiving side is different than the transmitted one. Actually the data is somehow not correctly trancieved. The schematic is in the attachment. Should i use some resistors or capacitors in vcc ground pins in order to make the transmission without error?

Thank you

0 mahmut turk over 11 years ago in reply to mahmut turk

Intellectual 300 points

0 Thomas Kugelstadt over 11 years ago in reply to mahmut turk

TI__Mastermind 28265 points

I hope you have buffered your transceiver supplies with 0.1uF at least?

what is it the ground potential difference between both transceivers?

0 mahmut turk over 11 years ago in reply to Thomas Kugelstadt

Intellectual 300 points

hello Thomas;

ground potential difference is 0. I didnt use any capacitors. But i will put capacitors in a minute. Could you refer an application note for me?

thank you.

0 Thomas Kugelstadt over 11 years ago in reply to mahmut turk

TI__Mastermind 28265 points

For each transceiver simply connect a 0.1uF ceramic capacitor veteen Vcc and GND. You don't need an application note for that.

Please send me a scope shot of your data.

Thank you, Thomas

0 mahmut turk over 11 years ago in reply to Thomas Kugelstadt

Intellectual 300 points

Hello Thomas,

I observed that the problem is not related to sn65hvd78. It was my fault that the transmitted data was not the one that ı was intended to send. When i corrected the data in front of the driver sn65hvd78, i observed the same data at ouput of receiver sn65hvd78.

Thanks for your help.

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sn65hvd78 data transmission problem