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Semiory

Zybo Board : Pmod to I/O (II)

Question

 

Hello experts,

I'd like to use the all signals of the pmods (excepted MIO pmod) as single ended lines. I have read the post:

 

however there are no description how to set the ports as a single ended lines. I have tried to make it straight forward in the ucf file as following:

NET "line1"           LOC=W19 | IOSTANDARD=LVCMOS33; #IO_L22N_T3_34                   
NET "line2"           LOC=W18 | IOSTANDARD=LVCMOS33; #IO_L22P_T3_34                

 

Unfortunately all signals with "N" (e.g. IO_L22N_T3_34) are set to -3.3V (MINUS 3.3V measured to ground) if I set the output "HIGH".

How can I use this differential pair as single ended with +3.3V (PLUS 3.3V) as HIGH output and (ZERO) 0V as "LOW". (Measured to ground)

Thanks in Advance

Edited by KaitlynFranz

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Your UCF code should work properly... try using the ucf above in a simple design that just ties line1 and line2 to sw0 and sw1. Then try toggling the switches and measure what happens on JB4_N and JB4_P using your multimeter. What do you measure when the switches are low, and what do you measure when they are high? 

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The Zynq can't generate a negative voltage - no negative voltages are supplied to the device, and the pins can only drive either from the bank voltage or 0V. Double check how you are metering things.

When used as a differential pair, one will always be switched to the high level, the other will be switched to the low level, so there can be + or - 3.3V between pins (assuming that the I/O bank is running at 3.3V), but no pin is actually less than 0V with respect to the board's ground.

The simplest cause is of seeing such results is that you are metering between two I/O pins because you have accidentally connected the GND probe to an active I/O line rather than GND. 

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Thanks All! I have foud the Problem... The Osci I get, was programmed by my colleague to be inverted and AC coupled.

This causes displayed voltages to be from +3 to -3 volts.

As a hint: always check hardware before use :)

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