Fujitsu Microelectronics Europe Application Note MCU-AN-390090-E-V10 F²MC-16LX FAMILY 16-BIT MICROCONTROLLER ALL SERIES EXTERNAL CLOCK AND RELOAD COUNTER APPLICATION NOTE External Clock and Reload Counter – Application Note Revision History Revision History Date 2003-04-24 2008-07-08 Issue V1.0; MWi; First version V1.1; MWi; Table of contents corrected This document contains 8 pages. 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Should one of the above stipulations be or become invalid and/or unenforceable, the remaining stipulations shall stay in full effect © Fujitsu Microelectronics Europe GmbH -3- MCU-AN-390090-E-V10 External Clock and Reload Counter – Application Note Contents Contents REVISION HISTORY.............................................................................................................. 2 WARRANTY AND DISCLAIMER........................................................................................... 3 CONTENTS ............................................................................................................................ 4 0 INTRODUCTION................................................................................................................ 5 1 PRINCIPAL DIFFICULTIES............................................................................................... 6 1.1 Clock Sampling ......................................................................................................... 6 2 RELOAD VALUE TABLES................................................................................................ 7 2.1 Deviation <1%........................................................................................................... 7 2.2 Deviation <2%........................................................................................................... 7 2.3 Deviation <3%........................................................................................................... 7 2.4 Deviation <4%........................................................................................................... 8 MCU-AN-390090-E-V10 -4- © Fujitsu Microelectronics Europe GmbH External Clock and Reload Timer – Application Note Introduction 0 Introduction When using an external clock source together with the dedicated reload counter of the LINUART not all possible settings are allowed. This application note gives an overview about most common external clock frequencies in subject to smallest usable reload value and resulting baud rate deviation. © Fujitsu Microelectronics Europe GmbH -5- MCU-AN-390090-E-V10 External Clock and Reload Counter – Application Note Chapter 1 Principal Difficulties 1 Principal Difficulties DESCRIPTION OF DIFFICULTIES IN SAMPLING EXTERNAL CLOCK SIGNALS 1.1 Clock Sampling The MCU clock and an independent external clock signal will neither be synchronous nor in phase. Thus some kind of jitter will always occur when the external signal is sampled. The following graphic illustrates this problem: MCU Clock External Clock Signal Sampled Clock SIgnal 4 cycles 4 cycles 5 cycles 4 cycles 4 cycles In the case above the external clock signal is slightly lower than the MCU clock divided by 8. This causes in subject of the deviation sometimes a sampled clock phase, which is one MCU clock cycle longer. Contrariwise if the external clock would be slightly higher, a 3-cycle sampled clock phase will sometimes occur. This jitter causes a baud rate deviation which decreases with the used reload value. The limit of the deviation is ±1 cycle for high reload values. For some combinations for MCU clock, external clock and reload value the resulting deviation will be so high, that accurate communication is either not guaranteed or not possible. The following tables in the next chapter give an overview for smallest reload value at different external serial clocks and MCU frequencies. MCU-AN-390090-E-V10 -6- © Fujitsu Microelectronics Europe GmbH External Clock and Reload Timer – Application Note Chapter 2 Reload Value Tables 2 Reload Value Tables RELOAD VALUE TABLES IN SUBJECT TO DEVIATION, MCU CLOCK AND EXT. CLOCK 2.1 Deviation <1% Ext. Clock (Hz) The following table entries contain the smallest usable reload value for resulting baud rates deviation better than 1%. 2.2 7,3728M 6M 5M 3,6864M 3M 1,8432M 1,5M 4M * * * * * 42 26 8M * * * 48 27 19 14 MCU Clock (Hz) 16M 20M 24M 42 32 28 26 21 5 25 5 17 19 13 13 14 11 5 10 8 7 6 6 5 32M 19 14 14 10 6 5 5 48M 13 5 9 7 5 5 5 * not possible Deviation <2% Ext. Clock (Hz) The following table entries contain the smallest usable reload value for resulting baud rates deviation better than 2%. 2.3 7,3728M 6M 5M 3,6864M 3M 1,8432M 1,5M 4M * * * * * 19 14 8M * * * 19 12 10 6 MCU Clock (Hz) 16M 20M 24M 19 15 13 15 9 5 12 5 7 10 8 7 6 6 5 5 5 5 5 5 5 32M 10 6 5 5 5 5 5 48M 7 5 5 5 5 5 5 * not possible Deviation <3% Ext. Clock (Hz) The following table entries contain the smallest usable reload value for resulting baud rates deviation better than 3%. 7,3728M 6M 5M 3,6864M 3M 1,8432M 1,5M 4M * * * * * 13 9 8M * * * 13 9 7 5 © Fujitsu Microelectronics Europe GmbH MCU Clock (Hz) 16M 20M 24M 13 11 9 9 6 5 7 5 5 6 6 5 5 5 5 5 5 5 5 5 5 -7- 32M 7 5 5 5 5 5 5 48M 5 5 5 5 5 5 5 * not possible MCU-AN-390090-E-V10 External Clock and Reload Counter – Application Note Chapter 2 Reload Value Tables 2.4 Deviation <4% Ext. Clock (Hz) The following table entries contain the smallest usable reload value for resulting baud rates deviation better than 4%. 7,3728M 6M 5M 3,6864M 3M 1,8432M 1,5M MCU-AN-390090-E-V10 4M * * * * * 8 6 8M * * * 8 6 5 5 MCU Clock (Hz) 16M 20M 24M 8 8 6 6 5 5 7 5 5 5 5 5 5 5 5 5 5 5 5 5 5 -8- 32M 5 5 5 5 5 5 5 48M 5 5 5 5 5 5 5 * not possible © Fujitsu Microelectronics Europe GmbH