AR# 50802

7 Series, UltraScale, and UltraScale+ - What state are the I/Os in at power up?

Description

In 7 Series, UltraScale, and UltraScale+ devices, what state are the I/Os in after all of the power rails are powered and before configuration?

Solution

The 7 Series, UltraScale and UltraScale+ FPGA data sheets state the following:

The recommended power-on sequence is VCCINT, VCCBRAM, VCCAUX, VCCAUX_IO, and VCCO to achieve minimum current draw and ensure that the I/Os are 3-stated at power-on.

The 7 Series, UltraScale, and UltraScale+ FPGAs contain a pin called PUDC_B. When PUDC_B is Low, internal pull-up resistors are enabled on each SelectIO pin.

When PUDC_B is High, internal pull-up resistors are disabled on each SelectIO pin. The state of this pin effects the state of the I/O from power-on until configuration completes. Therefore, the I/Os will be 3-stated after power-on when PUDC is High.

The state of the I/O prior to the rails being powered is not guaranteed.

Note: due to the presence of the clamp diode, if the I/Os are driven before Vcco is powered this will reverse bias the Vcco rail.

For further information, see (Xilinx Answer 45985).

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AR# 50802
Date 08/10/2020
Status Active
Type General Article
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