AVR512: Migration from ATmega48/88/168 to

AVR512: Migration from ATmega48/88/168 to
ATmega48P/88P/168P
Features
• General Porting Considerations
• Register and bit names
• Low-frequency Crystal / Timer/Counter Oscillator
8-bit
Microcontrollers
Application Note
1 Introduction
This application note summarizes the relevant differences when migrating from
ATmega48/88/168 to ATmega48P/88P/168P. For detailed information on the
devices please see the respective datasheets.
The ATmega48P/88P/168P is designed to be pin and functionality compatible with
ATmega48/88/168, but because of improvements mentioned in this application
note there may be a need for minor modifications in the application when migrating
from ATmega48/88/168 to ATmega48P/88P/168P.
For details on migrating between ATmega48P/88P/168P refer to the migration note
AVR®095: Migrating between ATmega48, ATmega88 and ATmega168.
Rev. 8035A-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);
DDR
&= ~(1<<PORTE5);
// Set pin 5 on port E high
// 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 ATmega48/88/168 and ATmega48P/88P/168P some register bits has been
added, but none of the existing bits has been removed, nor moved to different
locations.
4 Low-frequency Crystal / Timer/Counter Oscillator
The low frequency crystal oscillator of the ATmega48P/88P/168P is optimized for
very low power consumption thus the crystal driver strength is reduced compared to
the ATmega48/88/168. 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
ATmega164P/324P/644P low-frequency oscillator is typically 6pF, but the tracks to
the crystal will add some additional capacitance. Table 4-1 shows the ESR
recommendations for ATmega48P/88P/168P.
Table 4-1. ESR recommendation for 32.768 kHz crystals for ATmega48P/88P/168P.
Note:
Crystal CL [pF]
Max ESR1 [kΩ]
6.5
75
9
65
12.5
30
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 Appendix A.
2
AVR512
8035A-AVR-07/06
AVR512
The startup times are increased as shown in Table 4-2.
Table 4-2. Startup times with 32.768 kHz crystals.
Startup time2 [ms]
Atmega48/88/168
Startup time2 [ms]
Atmega48P/88P/168P
6.5
-
600
9
300
700
12.5
400
1700
Crystal CL [pF]
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.
5 Appendix A
Table 5-1 is a selection of crystals that meet the ESR requirements of the
ATmega48P/88P/168P. 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 ATmega48P/88P/168P low-frequency Crystal Oscillator.
Mounting
(SMD/HOLE)
Frequency
Tolerance [±ppm]
Load Capacitance
[pF]
Equivalent Series
Resistance (ESR)
[kΩ]
Vendor
Type
C-MAC
WATCH CRYSTALS
HOLE
20
6
50
C-MAC
85SMX
SMD
20
6
55
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
C-MAC
®
®
3
8035A-AVR-07/06
Mounting
(SMD/HOLE)
Frequency
Tolerance [±ppm]
Load Capacitance
[pF]
Equivalent Series
Resistance (ESR)
[kΩ]
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
®
4
AVR512
8035A-AVR-07/06
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8035A-AVR-07/06