Atmel ATmega645 Installation and operating instructions

Atmel AVR543: Migration from
ATmega645/6450/649/6490 to
ATmega645A/6450A/649A/6490A
1 Introduction
The Atmel®ATmega645A/6450A/649A/6490A is a functionally identical, drop-in
replacement for the Atmel ATmega645/6450/649/6490. All devices are subject to
the same qualification process and same set of production tests, but some
electrical characteristics differ.
ATmega645/6450/649/6490 and ATmega645A/6450A/649A/6490A have separate
datasheets. This application note outlines the differences between the two devices
and between the datasheets. There is also a detailed change log to assist the user
at the end of the ATmega645A/6450A/649A/6490A datasheet. Remember to
always use the latest revision of the device datasheet.
Minor differences in typical characteristics are not discussed in this document as
long as the low and high limits remain the same. For detailed information about the
typical characteristics, see sections “Electrical Characteristics” and “Typical
Characteristics” of the device datasheets.
Note: This application note serves as a guide to ease migration. For complete
device details, always refer to the most recent version of the
ATmega645A/6450A/649A/6490A datasheet.
8-bit Atmel
Microcontrollers
Application Note
Rev. 8423A-AVR-11/11

2 Atmel AVR543
8423A-AVR-11/11
2 Changes in characteristics
This section outlines such differences in characteristics that may have an effect on
the application in which the device is used. For detailed information, refer to the most
recent version of the device datasheets.
2.1 Reset
Table 2-1 summarizes the differences between the reset threshold parameters of
Atmel ATmega645/6450/649/6490 and Atmel ATmega645A/6450A/649A/6490A.
Table 2-1. Power-on reset threshold voltage.
ATmega645/6450/649/6490 ATmega645A/6450A/649A/6490A
Symbol
Min. Typ. Max. Min. Typ. Max.
Unit
VPOT rising 0.7 1.0 1.4 1.1 1.4 1.6 V
VPOT falling 0.05 0.9 1.3 0.6 1.3 1.6 V
2.2 JTAG ID
Table 2-2 summarizes the differences between the ATmega645/6450/649/6490 and
ATmega645A/6450A/649A/6490A JTAG IDs.
Table 2-2. JTAG ID.
JTAG ID
Part Part Number Manufacture ID
ATmega645 9605 0x1F
ATemga645A 960D 0x1F
ATmega6450 9606 0x1F
ATmega6450A 960E 0x1F
ATmega649 9603 0x1F
ATmega649A 960B 0x1F
ATemga6490 9604 0x1F
ATmega6490A 960C 0x1F
2.3 Low frequency crystal oscillator
In ATmega645A/6450A/649A/6490A the crystal driver strength of the Low Frequency
Crystal Oscillator is reduced compared to the ATmega645/6450/649/6490. This
means that when selecting a crystal, its load capacitance and Equivalent Series
Resistance (ESR) must be taken into consideration. Both values are specified by the
crystal vendor. The internal capacitance of the ATmega645A/6450A/649A/6490A low-
frequency oscillator is typically 6pF, but the tracks to the crystal will add some
additional capacitance. Table 2-3 shows the ESR recommendations for
ATmega645A/6450A/649A/6490A.

Atmel AVR543
3
8423A-AVR-11/11
Table 2-3. ESR recommendation for 32.768kHz crystals for Atmel
ATmega645A/6450A/649A/6490A.
Crystal CL [pF] Max ESR (1) [kΩ]
6.5 75
9.0 65
12.5 30
Note: 1. The values stated are for an oscillator allowance safety margin of 5. Since the
oscillator’s transconductance is temperature compensated one can use a safety
margin of 4, thus giving a max ESR of 90, 80 and 40kΩrespectively.
For examples of crystals that comply with the requirements, see Appendix A.
The startup times are increased as shown in Table 2-4.
Table 2-4. Startup times with 32.768kHz crystals.
Crystal CL [pF]
Startup time (1) [ms]
Atmel ATmega645/6450/649/6490
Startup time (1) [ms]
ATmega645A/6450A/649A/6490A
6.5 - 600
9.0 300 700
12.5 400 1700
Note: 1. Crystals usually need ~3000ms before they are completely stable with any
oscillator design. The time stated is before the crystal is running with a sufficient
amplitude and frequency stability.

4 Atmel AVR543
8423A-AVR-11/11
3 Datasheet changes
For a summary of changes, see the revision history at the end of the Atmel
ATmega645A/6450A/649A/6490A datasheet.

Atmel AVR543
5
8423A-AVR-11/11
4 Appendix A
Table 4-1 is a selection of crystals that meet the ESR requirements of the Atmel
ATmega645A/6450A/649A/6490A. The crystals are listed based on datasheet
information and are not tested with the actual device. Any other crystal that complies
with the ESR requirements can also be used. Availability and RoHS compliance has
not been investigated.
Table 4-1. Examples of crystals compliant with ATmega645A/6450A/649A/6490A low-frequency crystal oscillator.
Vendor Type
Mounting
(SMD/HOLE)
Frequency
Tolerance [±ppm]
Load Capacitance
[pF]
Equivalent Series
Resistance (ESR)
[kΩ]
C-MAC WATCH CRYSTALS HOLE 20 6 50
C-MAC 85SMX SMD 20 6 55
C-MAC 90SMX SMD 20 6 60
ECLIPTEK E4WC HOLE 20 6 50
ENDRICH 90SMX SMD 5 6 50
EPSON®C-001R HOLE 20 6 -> 12.5 (specify) 35
EPSON C-002RX HOLE 20 6 -> 10 (specify) 50
EPSON C-004R HOLE 20 6 -> 10 (specify) 50
EPSON C-005R HOLE 20 6 -> 10 (specify) 50
EPSON MC-30A SMD 20 6 -> 10 (specify) 50
EPSON MC-306 SMD 20 6 -> 10 (specify) 50
EPSON MC-405 SMD 20 6 -> 10 (specify) 50
EPSON MC-406 SMD 20 6 -> 10 (specify) 50
GOLLEDGE GWX HOLE 5 6, 8 or 12.5 35
GOLLEDGE GSWX-26 SMD 10 6 , 8 or 12.5 35
GOLLEDGE GDX1 HOLE 10 6 42
GOLLEDGE GSX-200 SMD 5 6 50
IQD WATCH CRYSTALS HOLE 20 6 50
IQD 90SMX HOLE 10 6 60
IQD 91SMX HOLE 10 6 60
MICROCRYSTAL MS3V-T1R HOLE 20 7 or 9 65
MICROCRYSTAL MS2V-T1R HOLE 20 7 or 9 65
MICROCRYSTAL CC4V-T1A SMD 30 9 65
MICROCRYSTAL CC1V-T1A SMD 30 9 60
MICROCRYSTAL CC7V-T1A SMD 30 9 70
MMD WC26 HOLE 8 8 35
MMD WC38 HOLE 8 8 35
MMD WC155 HOLE 8 8 40
MMD WCSMC SMD 20 6 50
OSCILENT SERIES 111 HOLE 10 6 or 12.5 30
OSCILENT SERIES 112 HOLE 10 6 or 12.5 40

6 Atmel AVR543
8423A-AVR-11/11
Vendor Type
Mounting
(SMD/HOLE)
Frequency
Tolerance [±ppm]
Load Capacitance
[pF]
Equivalent Series
Resistance (ESR)
[kΩ]
OSCILENT SERIES 113 HOLE 10 8 40
OSCILENT SERIES 223 SMD 20 6 50
RALTRON SERIES R38 HOLE 5 6 or 12.5 35
RALTRON SERIES R26 HOLE 5 6 or 12.5 35
RALTRON SERIES R145 HOLE 5 8 40
RALTRON SERIES RSE A, B, C, D SMD 20 6 50
SBTRON SBX-13 SMD 20 6 50
SBTRON SBX-20 SMD 20 6 50
SBTRON SBX-21 SMD 20 6 50
SBTRON SBX-24 SMD 20 6 50
SBTRON SBX-23 SMD 20 6 50
SBTRON SBX-22 SMD 20 6 50
SBTRON SBX-14 HOLE 20 6 50
SUNTSU SCT1 HOLE 20 6, 8, 10 or 12.5 40
SUNTSU SCT2 HOLE 20 6, 8, 10 50
SUNTSU SCT3 HOLE 20 6, 8, 10 50
SUNTSU SCP1 SMD 20 6 50
SUNTSU SCT2G SMD 20 6 or 10 50

8423A-AVR-11/11
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