I am doing some bare metal programming for a 8-bit microcontorller. The datasheet mentions that few of the GPIO pins have "True Open Drain" while the others have "High Sink Capability". What does it actually mean? I know GPIO pins can be of Open-Drain or Push pull type and I know whats the meaning of that. But what is the difference between just "Open-Drain" and "True Open Drain"? Also what is High Sink Capability?