The weak pull-up resistor is enabled for Cyclone®, Cyclone II, Cyclone III and Cyclone IV devices, after the device exits Power On Reset (POR) as indicated by the nSTATUS pin going high. The user I/O pins are tri-stated during power-up and during POR. Thus if VCCIO is powered before VCC and other POR monitored supplies, the I/O pins will be tri-stated without the weak pull-up resistor enabled.
Article ID: 000085785 Content Type: Troubleshooting Last Reviewed: 09/11/2012
When is the weak pull-up resistor enabled during power up for Cyclone III and Cyclone IV devices?
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