View detail for AVR532: Migration from ATmega48/88/168 to ATmega48A/88A/168A

AVR532: Migration from ATmega48/88/168 to
ATmega48A/88A/168A
1 Introduction
The ATmega48A/88A/168A is a functionally identical, drop-in replacement for the
ATmega48/88/168. All devices are subject to the same qualification process and
same set of production tests, but as the manufacturing process is not the same
some electrical characteristics differ.
8-bit
Microcontrollers
Application Note
ATmega48/88/168 and ATmega48A/88A/168A have separate datasheets. This
application note outlines the differences between the two devices and the
datasheets. There is also a detailed change log to assist the user at the end of the
ATmega48A/88A/168A 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
ATmega48A/88A/168A data sheet.
Rev. 8280A-AVR-12/09
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 data sheets.
2.1 Reset
The table below summarizes the differences between the reset threshold parameters
of ATmega48/88/168 and that of ATmega48A/88A/168A.
Table 2-4. Power-On Reset threshold voltage
Symbol
ATmega48/88/168
ATmega48A/88A/168A
Unit
Min
Typ
Max
Min
Typ
Max
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 TWI
If another interrupt (e.g., INT0) occurs during TWI Power-down address match and
wakes up the CPU in ATmega48/88/168, the TWI aborts operation and return to it’s
idle state.
This limitation is not present in ATmega48A/88A/168A
2.3 Analog MUX errata
In ATmega48A/88A/168A there is an errata affecting the analog MUXes. When
migrating from ATmega48/88/168 it must be checked if this errata will affect program
execution and the documented workaround should be applied.
See the errata section of the ATmega48A/88A/168A data sheet for details.
2.4 Low-frequency Crystal Oscillator
In ATmega48A/88A/168A the crystal driver strength of the Low Frequency Crystal
Oscillator 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 ATmega48A/88A/168A low-frequency oscillator is typically
6pF, but the tracks to the crystal will add some additional capacitance. Table 2-5
shows the ESR recommendations for ATmega48A/88A/168A.
2
AVR532
8280A-AVR-12/09
AVR532
Table 2-5. ESR recommendation for 32.768 kHz crystals for ATmega48A/88A/168A.
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 the comply with the requirements see Appendix A
The startup times are increased as shown in Table 2-6.
Table 2-6. Startup times with 32.768 kHz crystals.
Crystal CL [pF]
Startup time2 [ms]
Atmega48/88/168
Startup time2 [ms]
Atmega48A/88A/168A
6.5
-
600
Note:
9
300
700
12.5
400
1700
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.
3
8280A-AVR-12/09
3 Appendix A
Table 4-1 is a selection of crystals that meet the ESR requirements of the
ATmega48A/88A/168A. 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 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
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
C-MAC
®
®
4
AVR532
8280A-AVR-12/09
AVR532
Mounting
(SMD/HOLE)
Frequency
Tolerance [±ppm]
Load Capacitance
[pF]
Equivalent Series
Resistance (ESR)
[kΩ]
Vendor
Type
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
®
5
8280A-AVR-12/09
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8280A-AVR-12/09