Rainbow Electronics ATmega8515L - Manual (Page 34)

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ATmega8515(L)
2512A–AVR–04/02
Notes: 1. These options should only be used when not operating close to the maximum fre-
quency of the device, and only if frequency stability at start-up is not important for the
application. These options are not suitable for crystals.
2. These options are intended for use with ceramic resonators and will ensure fre-
quency stability at start-up. They can also be used with crystals when not operating
close to the maximum frequency of the device, and if frequency stability at start-up is
not important for the application.
Low-frequency Crystal
Oscillator To use a 32.768 kHz watch crystal as the clock source for the device, the Low-fre-
quency Crystal Oscillator must be selected by setting the CKSEL Fuses to “1001”. The
crystal should be connected as shown in Figure 18. By programming the CKOPT Fuse,
the user can enable internal capacitors on XTAL1 and XTAL2, thereby removing the
need for external capacitors. The internal capacitors have a nominal value of 36 pF.
When this Oscillator is selected, start-up times are determined by the SUT Fuses as
shown in Table 9.
Note: 1. These options should only be used if frequency stability at start-up is not important
for the application.
Table 9. Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
SUT1..0
Start-up Time
from Power-down
Additional Delay from
Reset (V
CC
= 5.0V) Recommended Usage
00 1K CK (1) 4.1 ms Fast rising power or BOD
enabled
01 1K CK (1) 65 ms Slowly rising power
10 32K CK 65 ms Stable frequency at start-up
11 Reserved