18.3.2 Alternate Functions of Port C

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

Table 18-6. Port C Pins Alternate Functions
Port Pin	Alternate Function
PC6	RESET (Reset pin)
PC5	ADC5 (ADC Input Channel 5) SCL (Two-wire Serial Bus Clock Line)
PC4	ADC4 (ADC Input Channel 4) SDA (Two-wire Serial Bus Data Input/Output Line)
PC3	ADC3 (ADC Input Channel 3)
PC2	ADC2 (ADC Input Channel 2)
PC1	ADC1 (ADC Input Channel 1)
PC0	ADC0 (ADC Input Channel 0)

The alternate pin configuration is as follows:

• RESET – 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.

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

• SCL/ADC5 – Port C, Bit 5

SCL, Two-wire Serial Interface Clock: When the TWEN bit in TWCR is set (one) to enable the Two-wire Serial Interface, pin PC5 is disconnected from the port and becomes the Serial Clock I/O pin for the Two-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.

PC5 can also be used as ADC input Channel 5. Note that ADC input channel 5 uses digital power.

• SDA/ADC4 – Port C, Bit 4

SDA, Two-wire Serial Interface Data: When the TWEN bit in TWCR is set (one) to enable the Two-wire Serial Interface, pin PC4 is disconnected from the port and becomes the Serial Data I/O pin for the Two-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.

PC4 can also be used as ADC input Channel 4. Note that ADC input channel 4 uses digital power.

• ADC3 – Port C, Bit 3

PC3 can also be used as ADC input Channel 3. Note that ADC input channel 3 uses analog power.

• ADC2 – Port C, Bit 2

PC2 can also be used as ADC input Channel 2. Note that ADC input channel 2 uses analog power.

• ADC1 – Port C, Bit 1

PC1 can also be used as ADC input Channel 1. Note that ADC input channel 1 uses analog power.

• ADC0 – Port C, Bit 0

PC0 can also be used as ADC input Channel 0. Note that ADC input channel 0 uses analog power.

The tables below relate the alternate functions of Port C to the overriding signals shown in figure Figure 18-5.

Table 18-7. Overriding Signals for Alternate Functions in PC6:PC4
Signal Name	PC6/RESET	PC5/SCL/ADC5	PC4/SDA/ADC4
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	0	0
DIEOV	0	0	0
DI	–	–	–
AIO	RESET INPUT	ADC5 INPUT / SCL INPUT	ADC4 INPUT / SDA INPUT

Table 18-8. Overriding Signals for Alternate Functions in PC3:PC0⁽¹⁾
Signal Name	PC3/A11	PC2/A10	PC1/A9	PC0/A8
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	0	0	0	0
DIEOV	0	0	0	0
DI	–	–	–	–
AIO	ADC3 INPUT	ADC2 INPUT	ADC1 INPUT	ADC0 INPUT

Note: 1. When enabled, the Two-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.