Configuration Handbook - Kamami.pl

Passive Serial ConfigurationWhen CONF_DONE is sensed low after configuration, the configurationdevice recognizes that the target device has not configured successfully;therefore, your system should not pull CONF_DONE low to delayinitialization. Instead, use the CLKUSR option to synchronize theinitialization of multiple devices that are not in the same configurationchain. Devices in the same configuration chain will initialize together iftheir CONF_DONE pins are tied together.1 If the optional CLKUSR pin is being used and nCONFIG is pulledlow to restart configuration during device initialization, youneed to ensure that CLKUSR continues toggling during the timenSTATUS is low (maximum of 40 µs).When the FPGA is in user-mode, a reconfiguration can be initiated bypulling the nCONFIG pin low. The nCONFIG pin should be low for at least8 µs. When nCONFIG is pulled low, the FPGA also pulls nSTATUS andCONF_DONE low and all I/O pins are tri-stated. Since CONF_DONE ispulled low, this will activate the configuration device since it will see itsnCS pin drive low. Once nCONFIG returns to a logic high state andnSTATUS is released by the FPGA, reconfiguration begins.Figure 7–2 shows how to configure multiple devices with a configurationdevice. This circuit is similar to the configuration device circuit for asingle device, except the APEX 20KE or APEX 20KC devices are cascadedfor multi-device configuration.7–8 Altera CorporationConfiguration Handbook, Volume 1 August 2005