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5741 Discussions

Bidirectional LVDS buffer "Can't place node -- node is a differential I/O node"

ADufl
Beginner
418 Views

Hello,

I'm trying to connect a sensor to EP4CE40F23C7 Cyclone IV E FPGA.

It's supposed to be connected to a bidirectional LVDS drivers, I did the proof of concept with a board with such drivers and it works.

I would like to achieve the same thing without the middle board. The board supporting the FPGA have some FPGA pins directly connected to 2.54mm header pin, including U9 (IO DIFFIO_B13p) and V8 (IO DIFFIO_B13n). I intanciated the buffer_lvds_bidir via the Quartus wizzard and connected as follows :

inst_buffer_lvds_bidir : buffer_lvds_bidir   port map(   datain => sl_DATA_DV_j404,   dataio => io_sensor_data_p,   dataio_b => io_sensor_data_n,   dataout => sl_DATA_RC_j404,   oe => sl_DE_j404,   oe_b => not(sl_DE_j404)   );  

Here is the *.qsf extract :

set_location_assignment PIN_V8 -to sensor_data_n

set_location_assignment PIN_U9 -to sensor_data_p

set_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to sensor_data_p[0]

set_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to sensor_data_n[0]

set_instance_assignment -name CURRENT_STRENGTH_NEW 8MA -to sensor_data_p[0]

set_instance_assignment -name CURRENT_STRENGTH_NEW 8MA -to sensor_data_n[0]

set_instance_assignment -name SLEW_RATE 2 -to sensor_data_n[0]

set_instance_assignment -name SLEW_RATE 2 -to sensor_data_p[0]

 

 

And what I get stopping Fitter step :

Error (176172): Can't place node "sensor_data_p[0]" -- node is a differential I/O node

Error (171000): Can't fit design in device

 

Could you please guide me to what is the matter ?

 

Thank you,

 

0 Kudos
5 Replies
YuanLi_S_Intel
Employee
146 Views

Hi Adrien,

 

It might be caused by pin assignment issue. Is it possible to share your design so that i can debug further?

 

Thank You.

ADufl
Beginner
146 Views

The pin assignment concerning the bidirectional LVDS signal is given in the form of the *.qsf extract. If a larger view of the design is needed, I may need to do some proofing beforehand.

Thinking about it, it appears to me that it doesn't do much sense to do LVDS with 3.3V IOs. Am I wrong ?

YuanLi_S_Intel
Employee
146 Views

Hi Adrian,

 

Yes, you must use LVDS I/O Standard instead of two LVTTL.

 

Thank You.

ADufl
Beginner
146 Views

Hello,

The matter is the IOs I have access to are in a 3.3V bank so I'm kind of stuck...

YuanLi_S_Intel
Employee
146 Views

I understand about the situation. But you will need to use LVDS I/O standard in order to use LVDS. Hope for your understanding.

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