11.4.2 Open-Drain Configuration (ODCx)

Each I/O pin can be individually configured for either normal digital output or open-drain output. This is controlled by the Open-Drain Control register, ODCx, associated with each I/O pin. If the ODCx bit for an I/O pin is a ‘1’, the pin acts as an open-drain output. If the ODCx bit for an I/O pin is a ‘0’, the pin is configured for a normal digital output (the ODCx bit is valid only for output pins). After a Reset, the status of all the bits of the ODCx register is set to ‘0’.

The open-drain feature allows the generation of outputs higher than Vdd (e.g., 5V) on any desired 5V tolerant pins by using external pull-up resistors. The maximum open-drain voltage allowed is the same as the maximum Vih specification. The ODCx register setting takes effect in all of the I/O modes, allowing the output to behave as an open-drain, even if a peripheral is controlling the pin. Although the user could achieve the same effect by manipulating the corresponding LATx and TRISx bits, this procedure will not allow the peripheral to operate in Open-Drain mode (except for the default operation of the I²C pins). Since I²C pins are already open-drain pins, the ODCx settings do not affect the I²C pins. Also, the ODCx settings do not affect the JTAG output characteristics as the JTAG scan cells are inserted between the ODCx logic and the I/O.