I'm abusing the Issue system to remind prospective users of the digital servo about an easy to overlook configuration step.
As shipped by OpalKelly the FPGA has FB2 installed. In this configuration +3.3 V is supplied to VCCO bank 0 which is suitable for single-ended IO. Differential signaling for IO on bank 0 requires +2.5 V supplied to the power pins for VCCO0. For the NIST Servo PCB, +2.5 V comes from net DVDD25 and is routed to the OpalKelly expansion connectors. Removing FB2 makes the OpalKelly use +2.5 V from the expansion connectors.
The github instructions indicate removal of FB2 is required. With FB2 installed, USB to FPGA communication is fine but the LVDS interface to ADCs and DACs is erratic. The GUI does not generate an error message.
I'm abusing the Issue system to remind prospective users of the digital servo about an easy to overlook configuration step.
As shipped by OpalKelly the FPGA has FB2 installed. In this configuration +3.3 V is supplied to VCCO bank 0 which is suitable for single-ended IO. Differential signaling for IO on bank 0 requires +2.5 V supplied to the power pins for VCCO0. For the NIST Servo PCB, +2.5 V comes from net DVDD25 and is routed to the OpalKelly expansion connectors. Removing FB2 makes the OpalKelly use +2.5 V from the expansion connectors.
The github instructions indicate removal of FB2 is required. With FB2 installed, USB to FPGA communication is fine but the LVDS interface to ADCs and DACs is erratic. The GUI does not generate an error message.