ATmega16A datasheet(60/352 Pages) ATMEL

60 / 352 page

8154B–AVR–07/09

ATmega16A

12.3.3

Alternate Functions of Port C

The Port C pins with alternate functions are shown in Table 12-9. If the JTAG interface is

enabled, the pull-up resistors on pins PC5(TDI), PC3(TMS) and PC2(TCK) will be activated

even if a reset occurs.

The alternate pin configuration is as follows:

• TOSC2 – Port C, Bit 7

TOSC2, Timer Oscillator pin 2: When the AS2 bit in ASSR is set (one) to enable asynchronous

clocking of Timer/Counter2, pin PC7 is disconnected from the port, and becomes the inverting

output of the Oscillator amplifier. In this mode, a Crystal Oscillator is connected to this pin, and

the pin can not be used as an I/O pin.

• TOSC1 – Port C, Bit 6

TOSC1, Timer Oscillator pin 1: When the AS2 bit in ASSR is set (one) to enable asynchronous

clocking of Timer/Counter2, pin PC6 is disconnected from the port, and becomes the input of the

inverting Oscillator amplifier. In this mode, a Crystal Oscillator is connected to this pin, and the

pin can not be used as an I/O pin.

• TDI – Port C, Bit 5

TDI, JTAG Test Data In: Serial input data to be shifted in to the Instruction Register or Data Reg-

ister (scan chains). When the JTAG interface is enabled, this pin can not be used as an I/O pin.

• TDO – Port C, Bit 4

TDO, JTAG Test Data Out: Serial output data from Instruction Register or Data Register. When

the JTAG interface is enabled, this pin can not be used as an I/O pin.

The TD0 pin is tri-stated unless TAP states that shifts out data are entered.

• TMS – Port C, Bit 3

TMS, JTAG Test Mode Select: This pin is used for navigating through the TAP-controller state

machine. When the JTAG interface is enabled, this pin can not be used as an I/O pin.

• TCK – Port C, Bit 2

TCK, JTAG Test Clock: JTAG operation is synchronous to TCK. When the JTAG interface is

enabled, this pin can not be used as an I/O pin.

Table 12-9.

Port C Pins Alternate Functions

Port Pin

Alternate Function

PC7

TOSC2 (Timer Oscillator Pin 2)

PC6

TOSC1 (Timer Oscillator Pin 1)

PC5

TDI (JTAG Test Data In)

PC4

TDO (JTAG Test Data Out)

PC3

TMS (JTAG Test Mode Select)

PC2

TCK (JTAG Test Clock)

PC1

SDA (Two-wire Serial Bus Data Input/Output Line)

PC0

SCL (Two-wire Serial Bus Clock Line)

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