PL I/O voltage configuration

[HPYan]

Hi Experts,

   I am very new to Zybo z7 board. I am trying to program PL (XC7Z010-1) Pmod JC I/O input and output to both 1.8V instead of 3.3V. According Xilinx Zynq-7000 datasheet, PL's Programmable I/O Blocks can be programmed ranging from 1.2V to 3.3V. In Vivado, I can select IO/std to LVCMOS18(Or whatever other than 3.3V), however the output from I/O are always measured at 3.3V regardless what options I have selected under I/O Std. What I am missing here?  

Edited January 4, 2023 by HPYan

[asmi]

2 hours ago, HPYan said:

Hi Experts,

   I am very new to Zybo z7 board. I am trying to program PL (XC7Z010-1) Pmod JC I/O input and output to both 1.8V instead of 3.3V. According Xilinx Zynq-7000 datasheet, PL's Programmable I/O Blocks can be programmed ranging from 1.2V to 3.3V. In Vivado, I can select IO/std to LVCMOS18(Or whatever other than 3.3V), however the output from I/O are always measured at 3.3V regardless what options I have selected under I/O Std. What I am missing here?  

You are missing the fact that voltage level is set up in hardware by the voltage applied to corresponding Vccio pins. Mismatching Vccio levels of hardware and bitstream can lead to physical damage of IO buffer cells.

[RyanW]

I had this same misunderstanding starting out. The voltage constraints are there to tell Vivado what voltage you have externally supplied to it. The only way to change the voltage on those IO banks is to physically change the incoming voltage source to the pins on the FPGA that supply those IO banks. Just glancing at the Zybo Z7, it doesn't seem to have a pin header switch or any other way to switch the bank voltages; and considering this is a dev-board, there's not really a good way to go in and hack away voltage supply to those pins. I know on the Zed Board, there are some bank voltages you can control with a pin header jumper, and there are probably some other boards that have that capability as well.

If you really need to use this board for this application at 1.8V. It seems digilent has a PMOD connector that could probably help you out. I don't know what your target data-rate is, but you can check to see of the chip can handle it by viewing the data sheet. (It seems to say max data rate for translating to 1.8V is 75 Mbps on the features page, but their charts are confusing as I'm calculating slightly higher).

Digilent PMOD Level Shifter:
https://digilent.com/shop/pmod-lvlshft-logic-level-shifter/

Digilent PMOD Level Shifter References:
https://digilent.com/reference/pmod/pmodlvlshft/reference-manual?redirect=1

TI SN74LVC1T45 Datasheet:
https://www.ti.com/lit/ds/symlink/sn74lvc1t45.pdf

[HPYan]

15 hours ago, asmi said:

You are missing the fact that voltage level is set up in hardware by the voltage applied to corresponding Vccio pins. Mismatching Vccio levels of hardware and bitstream can lead to physical damage of IO buffer cells.

Oh I see. Thanks

[HPYan]

8 hours ago, RyanW said:

I had this same misunderstanding starting out. The voltage constraints are there to tell Vivado what voltage you have externally supplied to it. The only way to change the voltage on those IO banks is to physically change the incoming voltage source to the pins on the FPGA that supply those IO banks. Just glancing at the Zybo Z7, it doesn't seem to have a pin header switch or any other way to switch the bank voltages; and considering this is a dev-board, there's not really a good way to go in and hack away voltage supply to those pins. I know on the Zed Board, there are some bank voltages you can control with a pin header jumper, and there are probably some other boards that have that capability as well.

If you really need to use this board for this application at 1.8V. It seems digilent has a PMOD connector that could probably help you out. I don't know what your target data-rate is, but you can check to see of the chip can handle it by viewing the data sheet. (It seems to say max data rate for translating to 1.8V is 75 Mbps on the features page, but their charts are confusing as I'm calculating slightly higher).

Digilent PMOD Level Shifter:
https://digilent.com/shop/pmod-lvlshft-logic-level-shifter/

Digilent PMOD Level Shifter References:
https://digilent.com/reference/pmod/pmodlvlshft/reference-manual?redirect=1

TI SN74LVC1T45 Datasheet:
https://www.ti.com/lit/ds/symlink/sn74lvc1t45.pdf

This is helpful. Thanks