A High-Keeper is used for Controller-to-Target and Target-to-Controller Bus handoff, as well as optionally when the Bus is idle (see Q22.1, "What are some of the I3C Bus conditions when the Bus is considered inactive?"). The High-Keeper may be a passive weak Pull-Up resistor on the Bus, or an active weak Pull-Up (or equivalent) in the Controller. The High-Keeper is only required to be strong enough to prevent system-leakage from pulling the Bus Low. At the same time, the High-Keeper for the SDA line must be weak enough that a Target with the minimum IOL driver can pull the SDA line Low within the trDA minimum period. The system designer is responsible for balancing these factors.
Note: A High-Keeper is required for both SDA and SCL. External High-Keepers might be required if the Active Controller’s High-Keeper is not adequate per specification Section 220.127.116.11. Additionally, if an I3C Bus has multiple Controller-capable Devices (i.e., one Primary Controller and one or more Secondary Controllers), then the Active Controller is responsible for managing the High-Keeper, and Controllers using the Controller Role Handoff Procedure are required to engage or disengage their High-Keepers at the defined times during this procedure (per Section 18.104.22.168).