Description

keywords: bscan, boundary, scan, bypass, pwrdwn, power, down, pull, up,

When the BYPASS command is issued, everything behaves as expected, but when the HIGH-Z command is issued, the device shuts down. Why?

Solution

There will need to be an external pull-up on the PWRDWN pin if the HIGH-Z command is going to be used (as opposed to the BYPASS command).

The HIGH-Z command will tri-state all of the IOBs, including the PWRDWN pin.

The PWRDWN pin is an unsupported feature that will shut down the device, and this pin will require a pullup.