Article ID: 000079727 Content Type: Troubleshooting Last Reviewed: 09/11/2012

Do I need to connect a pull-up or a pull-down resistor on the nCONFIG line when configuring in PS (Passive Serial) or Fast Passive Parallel (FPP) mode?

Environment

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Description

Yes, a pull-up or pull-down resistor helps keep the nCONFIG line in a known state when the external host (a Max® II CPLD or a microcontroller) is not driving the line (for example, during external host reprogramming or power-up where the I/O driving nCONFIG may be tri-stated). If a pull-up resistor is added to the nCONFIG line, the FPGA stays in user mode if the external host is being reprogrammed. If a pull-down resistor is added to the nCONFIG line, the FPGA goes into reset mode if the external host is being reprogrammed.

Whenever the nCONFIG line is released high, ensure the first DCLK and DATA are not driven unintentionally. Altera recommends to keep the nCONFIG line low if the external host or the FPGA is not ready for configuration.

Resolution

 

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