28.5.1 I/O Lines
The I/O lines of the PORT are mapped to pins of the physical device. The following naming scheme is used:
Each line bundle with up to 32 lines is assigned an identifier 'xy', with letter x=A, B, C… and two-digit number y=00, 01, …31. Examples: A24, C03.
PORT pins are labeled 'Pxy' accordingly, for example PA24, PC03. This identifies each pin in the device uniquely.
Each pin may be controlled by one or more peripheral multiplexer settings, which allow the pad to be routed internally to a dedicated peripheral function. When the setting is enabled, the selected peripheral has control over the output state of the pad, as well as the ability to read the current physical pad state. Refer to I/O Multiplexing and Considerations for details.
Each pin may be secured or non-secured, with secured pins only accessible by secure accesses.
Device-specific configurations may cause some lines (and the corresponding Pxy pin) not to be implemented.
References: