ATmega1284 Atmel Corporation, ATmega1284 Datasheet - Page 35

• Manufacturer Part Number: ATmega1284
• Manufacturer: Atmel Corporation

Specifications of ATmega1284

• Flash (kbytes): 128 Kbytes
• Pin Count: 44
• Max. Operating Frequency: 20 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 16
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 32
• Ext Interrupts: 32
• Usb Speed: No
• Usb Interface: No
• Spi: 3
• Twi (i2c): 1
• Uart: 2
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: No
• Crypto Engine: No
• Sram (kbytes): 16
• Eeprom (bytes): 4096
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 1.8 to 5.5
• Operating Voltage (vcc): 1.8 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 3
• Output Compare Channels: 6
• Input Capture Channels: 1
• Pwm Channels: 6
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

9.5
8272C–AVR–06/11
Low Frequency Crystal Oscillator
The Low-frequency Crystal Oscillator is optimized for use with a 32.768kHz watch crystal. When
selecting crystals, load capasitance and crystal’s Equivalent Series Resistance, ESR must be
t a k e n i n t o c o n s i d e r a t i o n . B o t h v a l u e s a r e s p e c i f i e d b y t h e c r y s t a l v e n d o r .
ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P oscillator is optimized for very low
power consumption, and thus when selecting crystals, see
ESR recommendations on 9pF and 12.5pF crystals.
Table 9-7.
Note:
The Low-frequency Crystal Oscillator provides an internal load capacitance, see
35
Table 9-8.
The capacitance (Ce + Ci) needed at each TOSC pin can be calculated by using:
where:
Ce - is optional external capacitors as described in
Ci - is is the pin capacitance in
CL - is the load capacitance for a 32.768kHz crystal specified by the crystal vendor.
C
Crystals specifying load capacitance (CL) higher than the ones given in the
35, require external capacitors applied as described in
Figure 9-3.
Crystals specifying load capacitance (CL) higher than listed in
external capacitors applied as described in
S
ATmega164A/164PA/324A/324PA/
at each TOSC pin.
- is the total stray capacitance for one TOSC pin.
644A/644PA/1284/1284P
2. These options are intended for use with ceramic resonators and will ensure frequency stability
1. Maximum ESR is typical value based on characterization
at start-up. They can also be used with crystals when not operating close to the maximum fre-
quency of the device, and if frequency stability at start-up is not important for the application.
Device
ATmega164A/PA/324A/PA/644A/PA/1284/P
Maximum ESR Recommendation for 32.768kHz Watch Crystal
Capacitance for Low-frequency Oscillator
Crystal Oscillator Connections
Crystal CL (pF)
12.5
9.0
Table 9-8 on page 35
32kHz Osc. Type
System Osc.
Ce
Timer Osc.
+
Ci
Figure 9-2 on page
=
2 CL
⋅
Figure 9-2 on page 32
–
Figure 9-2 on page
C
Cap (Xtal1/Tosc1)
s
Table 9-7 on page 35
18pF
6pF
32.
Max ESR [kΩ]
Table 9-8 on page
65
30
32.
Cap (Xtal2/Tosc2)
Table 9-8 on page
(1)
Table on page
for maximum
8pF
6pF
35, require
35