Rainbow Electronics ATtiny12 - Manual (Page 5)

5
ATtiny11/12
1006C–09/01
The ATtiny12 AVR is supported with a full suite of program and system development
tools including: macro assemblers, program debugger/simulators, in-circuit emulators,
and evaluation kits.
Pin Descriptions
VCC Supply voltage pin.
GND Ground pin.
Port B (PB5..PB0) Port B is a 6-bit I/O port. PB4..0 are I/O pins that can provide internal pull-ups (selected
for each bit). On ATtiny11, PB5 is input only. On ATtiny12, PB5 is input or open-drain
output. The port pins are tri-stated when a reset condition becomes active, even if the
clock is not running. The use of pins PB5..3 as input or I/O pins is limited, depending on
reset and clock settings, as shown below.
Notes: 1. “Used” means the pin is used for reset or clock purposes.
2. “-” means the pin function is unaffected by the option.
3. Input means the pin is a port input pin.
4. On ATtiny11, PB5 is input only. On ATtiny12, PB5 is input or open-drain output.
5. I/O means the pin is a port input/output pin.
XTAL1 Input to the inverting oscillator amplifier and input to the internal clock operating circuit.
XTAL2 Output from the inverting oscillator amplifier.
RESET Reset input. An external reset is generated by a low level on the RESET pin. Reset
pulses longer than 50 ns will generate a reset, even if the clock is not running. Shorter
pulses are not guaranteed to generate a reset.
Clock Options The device has the following clock source options, selectable by Flash fuse bits as
shown:
Table 2. PB5..PB3 Functionality vs. Device Clocking Options
Device Clocking Option PB5 PB4 PB3
External Reset Enabled Used (1) - (2) -
External Reset Disabled Input (3) /I/O (4) - -
External Crystal - Used Used
External Low-frequency Crystal - Used Used
External Ceramic Resonator - Used Used
External RC Oscillator - I/O (5) Used
External Clock - I/O Used
Internal RC Oscillator - I/O I/O
Table 3. Device Clocking Options Select
Device Clocking Option ATtiny11 CKSEL2..0 ATtiny12 CKSEL3..0
External Crystal/Ceramic Resonator 111 1111 - 1010
External Low-frequency Crystal 110 1001 - 1000
External RC Oscillator 101 0111 - 0101