Atmel ATmega644, ATmega644P Migration from ATmega644 to ATmega644P

AVR508: Migration from ATmega644 to

ATmega644P

Features

• General Porting Considerations

• Register and bit names

• Low-frequency Crystal and Timer/Counter Oscillator

1 Introduction

This application note summarizes the relevant differences when migrating from
ATmega644 to ATmega644P. For detailed information on the devices please see
the respective datasheets.

The ATmega644P is designed to be pin and functionality compatible with
ATmega644, but because of improvements mentioned in this application note there
may be a need for minor modifications in the application when migrating from
ATmega644 to ATmega644P.

Further an additional USART has been added making the ATmega644P fully
compatible with ATmega164P/324P.

8-bit
Microcontrollers

Application Note

Rev. 8038A-AVR-07/06

2 General Porting Considerations

To make the porting process as easy as possible, we recommend to always refer to
registers and bit positions using their defined names, as absolute addresses and
values may change from device to device. When porting a design it is then often just
necessary to include the correct definition file. Some examples are shown below.

PORTE |= (1<<PORTE5); // Set pin 5 on port E high
DDR &= ~(1<<PORTE5); // Set pin 5 on port E as input

// Configure USI
USICR = (1<<USISIE)|(0<<USIOIE)|(1<<USIWM1)|(0<<USIWM0)|
(1<<USICS1)|(0<<USICS0)|(0<<USICLK)|(0<<USITC);

To avoid conflicts with added features and register functionality, never access
registers that are marked as reserved. Reserved bits should always be written to zero
if accessed. This ensures forward compatibility, and added features will stay in their
default states when unused.

3 Register and bit names

Between ATmega644 and ATmega644P some register bits has been added, but
none of the existing bits has been removed, nor moved to different locations.

4 Low-frequency Crystal and Timer/Counter Oscillator

The low-frequency crystal / Timer/counter oscillator of the ATmega644P is optimized
for very low power consumption and thus the crystal driver strength is reduced
compared to the ATmega644. 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.
ESR recommendations for ATmega644P. The internal capacitance of ATmega644P
low-frequency oscillator is typically 6pF, but the tracks to the crystal will add some
additional capacitance.

Table 4-1. ESR recommendation for 32.768 kHz crystals for ATmega644P

Crystal CL [pF] Max ESR1 [kΩ]

6.5 75

9 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 40 kΩ respectively.

For examples of crystals that comply with the requirements see

Table 4-1 shows the

Appendix A.

2

AVR508

8038A-AVR-07/06

5 Appendix A

AVR508

The startup times are also increased as shown in Table 4-2.

Table 4-2. Startup times with 32.768 kHz crystals

Startup time

Crystal CL [pF]

6.5 - 600

9 300 700

12.5 400 1700

Note: 2. 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.

ATmega644

2

[ms]

Startup time2 [ms]

ATmega644P

Table 5-1 is a selection of crystals that meet the ESR requirements of the
ATmega644P. 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 5-1. Examples of crystals compliant with ATmega644P low-frequency Crystal Oscillator.

Equivalent Series

Mounting

Vendor Type

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

(SMD/HOLE)

Frequency

Tolerance [±ppm]

Load Capacitance

[pF]

Resistance (ESR)

[kΩ]

8038A-AVR-07/06

3

Equivalent Series

Mounting

Vendor Type

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

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

(SMD/HOLE)

Frequency

Tolerance [±ppm]

Load Capacitance

[pF]

Resistance (ESR)

[kΩ]

4

AVR508

8038A-AVR-07/06

Disclaimer

Atmel Corporation

2325 Orchard Parkway
San Jose, CA 95131, USA
Tel: [phone]
Fax: [phone]

Regional Headquarters

Europe

Atmel Sarl
Route des Arsenaux 41
Case Postale 80
CH-1705 Fribourg
Switzerland
Tel: [phone]
Fax: [phone]

Asia

Room 1219
Chinachem Golden Plaza
77 Mody Road Tsimshatsui
East Kowloon
Hong Kong
Tel: [phone]
Fax: [phone]

Japan

9F, Tonetsu Shinkawa Bldg.
1-24-8 Shinkawa
Chuo-ku, Tokyo 104-0033
Japan
Tel: [phone]
Fax: [phone]

Disclaimer: The information in this document is provided in connection with Atmel products. No license, express or implied, by estoppel or otherwise, to any
intellectual property right is granted by this document or in connection with the sale of Atmel products. EXCEPT AS SET FORTH IN ATMEL’S TERMS AND

CONDITIONS OF SALE LOCATED ON ATMEL’S WEB SITE, ATMEL ASSUMES NO LIABILITY WHATSOEVER AND DISCLAIMS ANY EXPRESS, IMPLIED
OR STATUTORY WARRANTY RELATING TO ITS PRODUCTS INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTY OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT. IN NO EVENT SHALL ATMEL BE LIABLE FOR ANY DIRECT, INDIRECT,
CONSEQUENTIAL, PUNITIVE, SPECIAL OR INCIDENTAL DAMAGES (INCLUDING, WITHOUT LIMITATION, DAMAGES FOR LOSS OF PROFITS, BUSINESS
INTERRUPTION, OR LOSS OF INFORMATION) ARISING OUT OF THE USE OR INABILITY TO USE THIS DOCUMENT, EVEN IF ATMEL HAS BEEN
ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. Atmel makes no representations or warranties with respect to the accuracy or completeness of the

contents of this document and reserves the right to make changes to specifications and product descriptions at any time without notice. Atmel does not make any
commitment to update the information contained herein. Unless specifically provided otherwise, Atmel products are not suitable for, and shall not be used in,
automotive applications. Atmel’s products are not intended, authorized, or warranted for use as components in applications intended to support or sustain life.

© 2006 Atmel Corporation. All rights reserved. Atmel®, logo and combinations thereof, Everywhere You Are® and AVR®, are the registered
trademarks of Atmel Corporation or its subsidiaries. Other terms and product names may be trademarks of others.

Atmel Operations

Memory

2325 Orchard Parkway
San Jose, CA 95131, USA
Tel: [phone]
Fax: [phone]

Microcontrollers

2325 Orchard Parkway
San Jose, CA 95131, USA
Tel: [phone]
Fax: [phone]

La Chantrerie
BP 70602
44306 Nantes Cedex 3, France
Tel: [phone]
Fax: [phone]

ASIC/ASSP/Smart Cards

Zone Industrielle
13106 Rousset Cedex, France
Tel: [phone]
Fax: [phone]

1150 East Cheyenne Mtn. Blvd.
Colorado Springs, CO 80906, USA
Tel: [phone]
Fax: [phone]

Scottish Enterprise Technology Park
Maxwell Building
East Kilbride G75 0QR, Scotland
Tel: [phone]
Fax: [phone]

RF/Automotive

Theresienstrasse 2
Postfach 3535
74025 Heilbronn, Germany
Tel: [phone]
Fax: [phone]

1150 East Cheyenne Mtn. Blvd.
Colorado Springs, CO 80906, USA
Tel: [phone]
Fax: [phone]

Biometrics/Imaging/Hi-Rel MPU/
High Speed Converters/RF Datacom

Avenue de Rochepleine
BP 123
38521 Saint-Egreve Cedex, France
Tel: [phone]
Fax: [phone]

Literature Requests

www.atmel.com/literature

8038A-AVR-07/06