Rainbow-electronics ATtiny28L Bedienungsanleitung PDF herunterladen (Seite 36)

ATtiny28L/V

1062E–10/01

I/O Ports All AVR ports have true read-modify-write functionality when used as general digital I/O

ports. This means that the direction of one port pin can be changed without unintention-

ally changing the direction of any other pin with the SBI and CBI instructions. The same

applies for changing drive value (if configured as output) or enabling/disabling of pull-up

resistors (if configured as input).

Port A Port A is a 4-bit I/O port. PA2 is output-only, while PA3, PA1 and PA0 are bi-directional.

Three I/O memory address locations are allocated for Port A, one each for the Data

– PINA, $19. The Port A Input Pins address is read-only, while the Data Register and

the Control Register are read/write. Compared to other output ports, the Port A output is

delayed one extra clock cycle.

Port pins PA0, PA1 and PA3 have individually selectable pull-up resistors. When pins

PA0, PA1 or PA3 are used as inputs and are externally pulled low, they will source cur-

rent if the internal pull-up resistors are activated. PA2 is output-only. The PA2 output

buffer can sink 25 mA and thus drive a high-current LED directly. This output can also

be modulated (see “Hardware Modulator” on page 29 for details).

Port A Data Register – PORTA

Port A Control Register –

PACR

• Bits 7..4 – Res: Reserved Bits

These bits are reserved bits in the ATtiny28 and always read as zero.

• Bit 3 – DDA3: Data Direction PA3

When DDA3 is set (one), the corresponding pin is an output pin. Otherwise, it is an input

pin.

• Bit 2 – PA2HC: PORTA2 High Current Enable

When the PA2HC bit is set (one), an additional driver at the output pin PA2 is enabled.

This makes it possible to sink 25 mA at V

= 1.8V (V

= 0.8V). When the PA2HC bit is

cleared (zero), PA2 can sink 15 mA at V

= 1.8V (V

= 0.8V).

• Bits 1, 0 – DDA1, DDA0: Data Direction PA1 and PA0

When DDAn is set (one), the corresponding pin is an output pin. Otherwise, it is an input

pin.

Bit 76543210

$1B

––––PORTA3 PORTA2 PORTA1 PORTA0 PORTA

Read/Write R R R R R/W R/W R/W R/W

Initial Value 0 0 0 0 0 1 0 0

Bit 76543210

$1A ––––DDA3 PA2HC DDA1 DDA0 PACR

Read/Write R R R R R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

1 2 ... 31 32 33 34 35 36 37 38 39 40 41 ... 74 75

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