Why is there a voltage drop in single-ended I/O standards when located on dedicated differential input pins on side I/O banks in Stratix® III devices for designs compiled in the Quartus® II software v8.0?

Description

The Quartus® II Software v8.0 incorrectly enables an internal resistor between two I/Os of a side bank dedicated differential input pair when each I/O is configured as single-ended and any of the following conditions are true:

• The current strength is not specified
• The input parallel on chip termination (OCT) option for the I/O is enabled
• The output series OCT option for the I/O is enabled

This problem affects only Stratix® III devices. 

If both I/Os in this pair are input-only, the internal resistor is enabled incorrectly only if the input parallel termination option for either input is enabled. This resistor may cause the I/O pin to malfunction when it is single-ended by reducing the complementary pin voltage.

Resolution

This problem is fixed beginning with the Quartus® II software v8.0 SP1. Get the latest service pack from the Download Center.

To correct this problem in the Quartus II Software v8.0, if you cannot upgrade to the latest service pack version, download and install patch 0.22 below.