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Altera_Forum
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17 years ago

Cyclone III user I/O stay LOW during JTAG configration

Hi,all I found all user I/Os became LOW during JTAG configruation in my situation. The device is Cyclone III 3C35. However, it is said that user I/Os must be tri-stated during JTAG configuration i...
Altera_Forum's avatar
Altera_Forum
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17 years ago

I never experienced a similar behaviour. The Cyclone III handbook states:

--- Quote Start ---

The user I/O pins and dual-purpose I/O pins have weak pull-up resistors which are always enabled (after POR) before and during configuration.

--- Quote End ---

I wonder, if there may be an option to cause a different behaviour through JTAG boundary scan instructions. But even if this would be the case, I can't imagine, that the Quartus Programmer uses other than known default settings.

Can it be, that external hardware is pulling-down the observed IOs?