Solution ID: rd01262005_839
Last Modified: Jul 17, 2007
Product Category: Devices
Product Area: Configuration (FPGA)
Product Sub-area: JTAG
Problem
Why was the CONFIG_IO JTAG instruction introduced in Quartus II programmer version 4.2 when attempting to configure the FPGA over JTAG and are there any consequences with this change?
Solution
Beginning in Quartus® II software version 4.2, the programmer issues the CONFIG_IO instruction before attempting to JTAG configure an FPGA device.Upon power up, the FPGA attempts to configure from the configuration device. If the configuration fails the FPGA will reset and retry configuration. If configuration continues to fail this will again reset the device and the FPGA will enter an infinite reconfiguration loop.
The only way to break this loop is to shift in the CONFIG_IO instruction over JTAG. The side effect of shifting CONFIG_IO is that it asserts the nCONFIG signal low causing nSTATUS to transition low which could cause a system failure if there is another configuration scheme on the board.
When you use Jam, it does not issue the CONFIG_IO instruction. Jam can be used with the Quartus II programmer in a similar manner as adding a POF file for JTAG.
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