I'm not sure if you're using 7-Series or UltraScale MIG but the functionality is the same for both.
The app_zq_req function is similar to the app_ref_req function in that when user ZQ is enabled you can drive the ZQ Calibration requests from the app_interface instead of letting the memory controller automatically schedule them. PG150 (UltraScale) talks about this in the Maintenance Commands section starting on page 135 or the User ZQ section in UG586 (7-Series) starting on page 171. If you don't enable user ZQ then you don't need to drive this pin.
I'm not sure if you're using 7-Series or UltraScale MIG but the functionality is the same for both.
The app_zq_req function is similar to the app_ref_req function in that when user ZQ is enabled you can drive the ZQ Calibration requests from the app_interface instead of letting the memory controller automatically schedule them. PG150 (UltraScale) talks about this in the Maintenance Commands section starting on page 135 or the User ZQ section in UG586 (7-Series) starting on page 171. If you don't enable user ZQ then you don't need to drive this pin.
User controlled ZQ Cal can be used to postpone a ZQ_Cal command until a point when you're not driving a heavy workload to the interface in order to improve the quality of service for the transactions. Normally the controller will schedule the ZQCal regardless of incoming traffic which can cause higher latency for a set of transactions which may need to have really high quality of service in your application. Overall this is an advanced technique and rarely used.
