General Porting Considerations Register names Low-frequency Crystal Ti

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General Porting Considerations Register names Low-frequency Crystal Ti

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AVR514: Migration from ATmega325 ATmega325P
General Porting Considerations Register names Low-frequency Crystal Timer/Counter Oscillator
8-bit Microcontrollers Application Note
Introduction
This application note summarizes relevant differences when migrating from ATmega325 ATmega325P. detailed information devices please respective datasheets. ATmega325P designed functionality compatible with ATmega325, because improvements mentioned this application note there need minor modifications application when migrating from ATmega325 ATmega325P.
Rev. 8063A-AVR-03/07
General Porting Considerations
make porting process easy possible, recommend always refer registers positions using their defined names, absolute addresses values change from device device. When porting design then often just necessary include correct definition file. Some examples shown below.
PORTE (1<<PORTE5); ~(1<<PORTE5); port high port input
Configure USICR
avoid conflicts with added features register functionality, never access registers that marked reserved. Reserved bits should always written zero accessed. This ensures forward compatibility, added features will stay their default states when unused.
Register names
Between ATmega325 ATmega325P some register bits been added, none existing bits been removed, moved different locations.
Low-frequency Crystal Timer/Counter Oscillator
low-frequency crystal oscillator ATmega325P different from ATmega325. optimized very power consumption thus crystal driver strength reduced compared ATmega325. This means that when selecting crystal, load capacitance Equivalent Series Resistance (ESR) must taken into consideration. Both values specified crystal vendor. Table shows recommendations ATmega325P. internal capacitance ATmega325P oscillator typically tracks crystal will some additional capacitance. Table 4-1. recommendations 32.768 crystals ATmega325P
Crystal [pF] 12.5 Note: [k]1
values stated oscillator allowance safety margin Since oscillator's transconductance temperature compensated safety margin thus giving respectively.
examples crystals that comply with requirements Appendix
AVR514
8063A-AVR-03/07
AVR514
startup times also increased shown Table 4-2. Table 4-2. Startup times with 32.768 crystals ATmega325P.
Crystal [pF] 12.5 Note: Startup time(2) [ms] Atmega325 Startup time(2) [ms] Atmega325P 1700
Crystals usually need ~3000 before they completely stable with oscillator design. time stated before crystal running with sufficient amplitude frequency stability.
Appendix
Table selection crystals that ATmega325P. crystals listed based tested with actual device. other requirements also used. Availability investigated. meet requirements datasheet information crystal that complies with RoHS compliance been
Table 5-1. Examples crystals compliant with ATmega325P low-frequency Crystal Oscillator.
Mounting (SMD/HOLE) HOLE HOLE HOLE HOLE HOLE HOLE HOLE HOLE HOLE HOLE HOLE Frequency Tolerance [±ppm] Load Capacitance [pF] 12.5 (specify) (specify) (specify) (specify) (specify) (specify) (specify) (specify) 12.5 12.5 Equivalent Series Resistance (ESR)
Vendor C-MAC C-MAC C-MAC ECLIPTEK ENDRICH EPSON EPSON EPSON EPSON EPSON EPSON EPSON EPSON GOLLEDGE GOLLEDGE GOLLEDGE GOLLEDGE
Type WATCH CRYSTALS 85SMX 90SMX E4WC 90SMX C-001R C-002RX C-004R C-005R MC-30A MC-306 MC-405 MC-406 GSWX-26 GDX1 GSX-200 WATCH CRYSTALS 90SMX 91SMX
8063A-AVR-03/07
Vendor MICROCRYSTAL MICROCRYSTAL MICROCRYSTAL MICROCRYSTAL MICROCRYSTAL OSCILENT OSCILENT OSCILENT OSCILENT RALTRON RALTRON RALTRON RALTRON SBTRON SBTRON SBTRON SBTRON SBTRON SBTRON SBTRON SUNTSU SUNTSU SUNTSU SUNTSU SUNTSU
Type MS3V-T1R MS2V-T1R CC4V-T1A CC1V-T1A CC7V-T1A WC26 WC38 WC155 WCSMC SERIES SERIES SERIES SERIES SERIES SERIES SERIES R145 SERIES SBX-13 SBX-20 SBX-21 SBX-24 SBX-23 SBX-22 SBX-14 SCT1 SCT2 SCT3 SCP1 SCT2G
Mounting (SMD/HOLE) HOLE HOLE HOLE HOLE HOLE HOLE HOLE HOLE HOLE HOLE HOLE HOLE HOLE HOLE HOLE
Frequency Tolerance [±ppm]
Load Capacitance [pF] 12.5 12.5 12.5 12.5 12.5
Equivalent Series Resistance (ESR)
AVR514
8063A-AVR-03/07
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8063A-AVR-03/07

General Porting Considerations Register names Low-frequency Crystal Ti

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