In our application, we have an FPGA with a Nios processor programming a second (downstream) FPGA in Passive Serial mode. I've recently redesigned this downstream board and am finding that the downstream board is unable to configure, given that the nStatus pin is never released by the downstream board.
The downstream FPGA is a cyclone IV E series 144 pin qfp EP4ce22e22c7n.
Furthermore, I know that at least one IO pin is not tri-stated on power up, but driving low with an impedance of 300 ohms.
Visual inspection shows that all FPGA pins are well-soldered. The 1.2V VCCInt and VCCD_PLL rails and 2.5V VCCIO and VCCA rails are at appropriate and stable voltages. The newest rev board's power connections to the FPGA are identical to the working older rev's, and the FPGA isn't soldered on backwards or anything like that.
The problem persisted when the FPGA was desoldered and a new chip was soldered in its place.
Does anyone have an idea as to what could cause these symptoms?
