Alternate Functions of Port C

The Port C pins with alternate functions are shown in the table below:

Table 1. Port C Pins Alternate Functions
Port Pin	Alternate Function
PC6	RESET (Reset pin) PCINT14 (Pin Change Interrupt 14)
PC5	ADC5 (ADC Input Channel 5) SCL (2-wire Serial Bus Clock Line) PCINT13 (Pin Change Interrupt 13)
PC4	ADC4 (ADC Input Channel 4) SDA (2-wire Serial Bus Data Input/Output Line) PCINT12 (Pin Change Interrupt 12)
PC3	ADC3 (ADC Input Channel 3) PCINT11 (Pin Change Interrupt 11)
PC2	ADC2 (ADC Input Channel 2) PCINT10 (Pin Change Interrupt 10)
PC1	ADC1 (ADC Input Channel 1) PCINT9 (Pin Change Interrupt 9)
PC0	ADC0 (ADC Input Channel 0) PCINT8 (Pin Change Interrupt 8)

The alternate pin configuration is as follows:

RESET/PCINT14 – Port C, Bit 6
- RESET: Reset pin. When the RSTDISBL Fuse is programmed, this pin functions as a normal I/O pin, and the part will have to rely on Power-on Reset and Brown-out Reset as its reset sources. When the RSTDISBL Fuse is unprogrammed, the reset circuitry is connected to the pin, and the pin can not be used as an I/O pin.
- PCINT14: Pin Change Interrupt source 14. The PC6 pin can serve as an external interrupt source.

If PC6 is used as a reset pin, DDC6, PORTC6 and PINC6 will all read 0.

SCL/ADC5/PCINT13 – Port C, Bit 5
- SCL: 2-wire Serial Interface Clock. When the TWEN bit in TWCR is set (one) to enable the 2-wire Serial Interface, pin PC5 is disconnected from the port and becomes the Serial Clock I/O pin for the 2-wire Serial Interface. In this mode, there is a spike filter on the pin to suppress spikes shorter than 50 ns on the input signal, and the pin is driven by an open drain driver with slew-rate limitation.
- PCINT13: Pin Change Interrupt source 13. The PC5 pin can serve as an external interrupt source.
- PC5 can also be used as ADC input Channel 5. The ADC input channel 5 uses digital power.

SDA/ADC4/PCINT12 – Port C, Bit 4
- SDA: 2-wire Serial Interface Data. When the TWEN bit in TWCR is set (one) to enable the 2-wire Serial Interface, pin PC4 is disconnected from the port and becomes the Serial Data I/O pin for the 2-wire Serial Interface. In this mode, there is a spike filter on the pin to suppress spikes shorter than 50 ns on the input signal, and the pin is driven by an open drain driver with slew-rate limitation.
- PCINT12: Pin Change Interrupt source 12. The PC4 pin can serve as an external interrupt source.
- PC4 can also be used as ADC input Channel 4. The ADC input channel 4 uses digital power.

ADC3/PCINT11 – Port C, Bit 3
- PC3 can also be used as ADC input Channel 3. The ADC input channel 3 uses analog power.
- PCINT11: Pin Change Interrupt source 11. The PC3 pin can serve as an external interrupt source.

ADC2/PCINT10 – Port C, Bit 2
- PC2 can also be used as ADC input Channel 2. The ADC input channel 2 uses analog power.
- PCINT10: Pin Change Interrupt source 10. The PC2 pin can serve as an external interrupt source.

ADC1/PCINT9 – Port C, Bit 1
- PC1 can also be used as ADC input Channel 1. The ADC input channel 1 uses analog power.
- PCINT9: Pin Change Interrupt source 9. The PC1 pin can serve as an external interrupt source.

ADC0//CINT8 – Port C, Bit 0
- PC0 can also be used as ADC input Channel 0. The ADC input channel 0 uses analog power.
- PCINT8: Pin Change Interrupt source 8. The PC0 pin can serve as an external interrupt source.

The tables below relate the alternate functions of Port C to the overriding signals shown in Figure 1.

Table 2. Overriding Signals for Alternate Functions in PC6...PC4⁽¹⁾
Signal Name	PC6/RESET/PCINT14	PC5/SCL/ADC5/PCINT13	PC4/SDA/ADC4/PCINT12
PUOE	RSTDISBL	TWEN	TWEN
PUOV	1	PORTC5 • PUD	PORTC4 • PUD
DDOE	RSTDISBL	TWEN	TWEN
DDOV	0	SCL_OUT	SDA_OUT
PVOE	0	TWEN	TWEN
PVOV	0	0	0
DIEOE	RSTDISBL + PCINT14 • PCIE1	PCINT13 • PCIE1 + ADC5D	PCINT12 • PCIE1 + ADC4D
DIEOV	RSTDISBL	PCINT13 • PCIE1	PCINT12 • PCIE1
DI	PCINT14 INPUT	PCINT13 INPUT	PCINT12 INPUT
AIO	RESET INPUT	ADC5 INPUT / SCL INPUT	ADC4 INPUT / SDA INPUT

Note: 1. When enabled, the 2-wire Serial Interface enables slew-rate controls on the output pins PC4 and PC5. This is not shown in the figure. In addition, spike filters are connected between the AIO outputs shown in the port figure and the digital logic of the TWI module.

Table 3. Overriding Signals for Alternate Functions in PC3...PC0
Signal Name	PC3/ADC3/ PCINT11	PC2/ADC2/ PCINT10	PC1/ADC1/ PCINT9	PC0/ADC0/ PCINT8
PUOE	0	0	0	0
PUOV	0	0	0	0
DDOE	0	0	0	0
DDOV	0	0	0	0
PVOE	0	0	0	0
PVOV	0	0	0	0
DIEOE	PCINT11 • PCIE1 + ADC3D	PCINT10 • PCIE1 + ADC2D	PCINT9 • PCIE1 + ADC1D	PCINT8 • PCIE1 + ADC0D
DIEOV	PCINT11 • PCIE1	PCINT10 • PCIE1	PCINT9 • PCIE1	PCINT8 • PCIE1
DI	PCINT11 INPUT	PCINT10 INPUT	PCINT9 INPUT	PCINT8 INPUT
AIO	ADC3 INPUT	ADC2 INPUT	ADC1 INPUT	ADC0 INPUT