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rsgrimes
Observer
Observer
439 Views
Registered: ‎10-15-2009

Two output signals on two different pins appear to be added together! (Zync XC7Z010)

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I am trying to create a simple VHDL component that sends the output of a quadrature encoder on two pins (i.e. Phase A and Phase B). The component works, as illustrated here in the Vivado simulator:

SimulationSimulation

However, when I route those signals to two pins on my FPGA, using these constraints:

set_property PACKAGE_PIN G17 [get_ports {P_PHASE_A}];
set_property PACKAGE_PIN G18 [get_ports {P_PHASE_B}];
set_property IOSTANDARD LVCMOS33 [get_ports -of_objects [get_iobanks 35]];
 
I see the following on my scope:
 

Scope TracesScope Traces

It appears as if the two signals from my component are added together and sent to both pins! I suspect there is something I'm missing in the constaints file, as the two pins G17 and G18 apparently can be combined as an LVDS signal, which could explain what I am seeing; however, other signals on other LVDS-capable signals do not seem to exhibit the same behavior.

I am using a MicroZed 7010 (with XC7Z010-1CLG400C FPGA), mated with the AES-MBCC-IO-G I/O expander board, which simply brings the pins out to headers.

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bruce_karaffa
Scholar
Scholar
330 Views
Registered: ‎06-21-2017

The two pins are almost certainly shorted together somewhere.  They are not connected inside the FPGA.  I don't see anything in the schematic for the Microzed or expander board to account for this. 

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4 Replies
chaitusvk
Adventurer
Adventurer
396 Views
Registered: ‎02-15-2019

Use ila core to Debug 

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mage
Explorer
Explorer
365 Views
Registered: ‎05-25-2016

Do you set the VCCO_35 to 3.3V?

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bruce_karaffa
Scholar
Scholar
331 Views
Registered: ‎06-21-2017

The two pins are almost certainly shorted together somewhere.  They are not connected inside the FPGA.  I don't see anything in the schematic for the Microzed or expander board to account for this. 

View solution in original post

rsgrimes
Observer
Observer
224 Views
Registered: ‎10-15-2009

Embarrassed to admit, it was my scope probes that had shifted and caused the behavior! Doh! Thanks for prompting me to check another time.

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