ATtiny167-ESSZ datasheet(30/282 Pages) ATMEL

30 / 282 page

7728D–AVR–07/09

ATtiny87/ATtiny167

Figure 4-3.

Low-frequency Crystal Oscillator Connections

When this oscillator is selected, start-up times are determined by the SUT fuses or by CSUT

field as shown in Table 4-8.

Notes:

1. Flash Fuse bits.

2. CLKSELR register bits.

3. These options should only be used if frequency stability at start-up is not important for the

application.

4.2.6

External Clock

To drive the device from this external clock source, CLKI should be driven as shown in Figure

4-4. To run the device on an external clock, the CKSEL Fuses or CSEL field must be pro-

grammed as shown in Table 4-1 on page 25.

Figure 4-4.

External Clock Drive Configuration

When this clock source is selected, start-up times are determined by the SUT Fuses or CSUT

field as shown in Table 4-9.

This external clock can be used by the asynchronous timer if the high or low frequency Crystal

Oscillator is not running (See ”Enable/Disable Clock Source” on page 32.). The asynchronous

timer is then able to enable this input.

Table 4-8.

Start-up Times for the Low Frequency Crystal Oscillator Clock Selection

SUT1..0(1)

CSUT1..0(2)

Start-up Time from

Power-down/save

Additional Delay from

Reset (Vcc = 5.0V)

Recommended usage

1K (1024) CK(3)

4.1 ms

Fast rising power or BOD enabled

1K (1024) CK(3)

65 ms

Slowly rising power

32K (32768) CK

65 ms

Stable frequency at start-up

Reserved

XTAL2

XTAL1

GND

C1=12-22 pF

32.768 KHz

12-22 pF capacitors may be necessary if parasitic

impedance (pads, wires & PCB) is very low.

C2=12-22 pF

(XTAL2)

(CLKO)

CLKI

(XTAL1)

GND

External

Clock

Signal

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