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
PC7	TOSC2 (Timer Oscillator pin 2) PCINT23 (Pin Change Interrupt 23)
PC6	TOSC1 (Timer Oscillator pin 1) PCINT22 (Pin Change Interrupt 22)
PC5	ACO TDI (JTAG Test Data Input) PCINT21 (Pin Change Interrupt 21)
PC4	OC4A (Timer/Counter 4 Output Compare Match A Output) TDO (JTAG Test Data Output) PCINT20 (Pin Change Interrupt 20)
PC3	ICP4 (Timer/Counter4 Input Capture Trigger) TMS (JTAG Test Mode Select) PCINT19 (Pin Change Interrupt 19)
PC2	T4 (Timer/Counter 4 External Counter Input) TCK (JTAG Test Clock) PCINT18 (Pin Change Interrupt 18)
PC1	SDA0 (two-wire Serial Bus0 Data Input/Output Line) PCINT17 (Pin Change Interrupt 17)
PC0	SCL0 (two-wire Serial Bus0 Clock Line) PCINT16 (Pin Change Interrupt 16)

The alternate pin configuration is as follows:

TOSC2/PCINT23 – Port C, Bit 7
- TOSC2, Timer Oscillator pin 2. The PC7 pin can serve as an external interrupt source to the MCU.
- PCINT23: Pin Change Interrupt source 23. The PC7 pin can serve as an external interrupt source.
TOSC1/PCINT22 – Port C, Bit 6
- TOSC1, Timer Oscillator pin 1. The PC6 pin can serve as an external interrupt source to the MCU.
- PCINT22: Pin Change Interrupt source 22. The PC6 pin can serve as an external interrupt source.

TDI/PCINT21 – Port C, Bit 5
- TDI: JTAG Test Data Input
- PCINT21: Pin Change Interrupt source 21. The PC5 pin can serve as an external interrupt source.

OC4A/TDO/PCINT20 – Port C, Bit 4
- OC4A: Timer/Counter 4 Output Compare Match A Output
- TDO: JTAG Test Data Output
- PCINT20: Pin Change Interrupt source 20. The PC4 pin can serve as an external interrupt source.

TMS/ICP4/PCINT19 – Port C, Bit 3
- TMS: JTAG Test Mode Select
- ICP4: Timer/Counter4 Input Capture Trigger
- PCINT19: Pin Change Interrupt source 19. The PC3 pin can serve as an external interrupt source.

TCK/T4/PCINT18 – Port C, Bit 2
- TCK: JTAG Test Clock
- T4: Timer/Counter 4 External Counter Input
- PCINT18: Pin Change Interrupt source 18. The PC2 pin can serve as an external interrupt source.

SDA0/PCINT17 – Port C, Bit 1
- SDA0: two-wire Serial Bus0 Data Input/Output Line
- PCINT17: Pin Change Interrupt source 17. The PC1 pin can serve as an external interrupt source.

SCL0/PCINT16 – Port C, Bit 0
- SCL0: two-wire Serial Bus0 Clock Line
- PCINT16: Pin Change Interrupt source 16. 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 PC7...PC4
Signal Name	PC7/TOSC2/PCINT23	PC6/TOSC1/PCINT22	PC5/TDI/PCINT21	PC4/OC4A/TDO/PCINT20
PUOE	AS2 • EXCLK	AS2	JTAGEN	JTAGEN
PUOV	0	0	1	1
DDOE	AS2 • EXCLK	AS2	JTAGEN	JTAGEN OC4A ENABLE
DDOV	0	0	0	SHIFT_IR + SHIFT_DR + OC4A
PVOE	0	0	0	JTAGEN
PVOV	0	0	0	TDO
DIEOE	AS2 • EXCLK + PCINT23 • PCIE2	AS2 + PCINT22 • PCIE2	JTAGEN + PCINT21 • PCIE2	JTAGEN + PCINT20 • PCIE2
DIEOV	AS2	EXCLK + AS2	JTAGEN	JTAGEN
DI	PCINT23 INPUT	PCINT22 INPUT	PCINT21 INPUT	PCINT20 INPUT
AIO	T/C2 OSC OUTPUT	T/C1 OSC INPUT	TDI INPUT	-

Table 3. Overriding Signals for Alternate Functions in PC3...PC0
Signal Name	PC3/TMS/ICP4/PCINT19	PC2/T4/PCINT18	PC1/SDA0/PCINT17	PC0/SCL0/PCINT16
PUOE	JTAGEN	JTAGEN	TWEN	TWEN
PUOV	1	1	PORTC1 • PUD	PORTC0 • PUD
DDOE	JTAGEN	JTAGEN	TWEN	TWEN
DDOV	0	0	0	0
PVOE	0	0	TWEN	TWEN
PVOV	0	0	SDA OUT	SCL OUT
DIEOE	JTAGEN + PCINT19 • PCIE2	JTAGEN + PCINT18 • PCIE2	PCINT17 • PCIE2	PCINT16 • PCIE2
DIEOV	JTAGEN	JTAGEN	1	1
DI	ICP4 INPUT PCINT19 INPUT	T4 INPUT PCINT18 INPUT	PCINT17 INPUT	PCINT16 INPUT
AIO	TMS INPUT	TCK INPUT	SDA0 INPUT	SCL0 INPUT