EB371 Considerations Programming System Clock Frequency MC68HC16
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EB371
Considerations Programming System Clock Frequency MC68HC16 MC68300 Devices
Charles Melear Microcontroller Division Austin, Texas
Introduction
MC68HC16 MC68300 Families microcontrollers (MCU) derive internal system clock from either external clock source output internal PLL/VCO (phase-locked loop/voltage-controlled oscillator). MODCK held release reset, clock signal applied EXTAL will system clock frequency. MODCK held high release reset, system clock frequency will output PLL/VCO.
Frequency
frequency controlled programming SYNCR (clock synthesizer control register).
Figure SYNCR Register FA04
Motorola, Inc., 2000
EB371
Engineering Bulletin
maximum frequency must limited greater than times maximum rated clock speed device MC68HC16 MC68300 Families. instance, MC68332ACFT16 rated maximum speed 16.7 MHz. Therefore, maximum speed 33.4 MHz. Likewise, device rated 20.97 would allow maximum speed 41.94 MHz, device rated 25.16 would allow maximum speed 50.32 MHz. When low-frequency crystal used, EXTAL input feeds input into PLL/VCO. Nominally, 32.768-kHz crystal external clock source used. When high-frequency crystal external clock source applied EXTAL pin, this input divided then applied PLL/VCO. When 4.194304-MHz crystal used, internal divide-by-128 EXTAL produces 32.768-kHz which then applied PLL/VCO. low-frequency crystal (approximately kHz), these equations apply: FSystem FCrystal[4(Y+1)(22W FVCO FSystem(2 high-frequency crystal (approximately MHz), these equations apply: FSystem (FCrystal/128)[4(Y+1)(22W FVCO FSystem(2
Bits SYNCR
bits control frequency system clock. bits control feedback prescaler VCO. output divide-by-2 circuit whose output drives internal system clock bus. divide-by-2 circuit bypassed that full frequency applied internal system clock bus.
EB371 MOTOROLA
Engineering Bulletin Introduction
internal system clock driven one-half speed VCO. other words, operate times frequency generate particular system clock frequency than
bits control feedback divider VCO. controls divide-by-4 feedback chain. frequency will multiplied four. example, system clock frequency 2.097 will obtained 001111 combination 000011. possible program combination SYNCR register. However, some possible combinations will cause specification violations. instance: bits cannot exceed binary value %001111. 111111 001111, system clock frequency 8.389 will obtained.
both cases, frequency will four times system clock frequency 33.554 MHz. This maximum allowable frequency device rated with system clock speed 16.777 MHz. bits exceed binary value %001111, will speed that exceeds maximum rating.
Permissible Values
Tables this document show permissible values 16-, 25-MHz devices. value that table will cause frequency above maximum allowable specification. Using numbers Table Table Table obtain clock frequency, find counter modulus leftmost column, then look appropriate prescaler cell. Empty cells represent values that exceed maximum system frequency specifications cause internal PLL/VCO exceed maximum frequency specifications MC68300 MC68HC16 devices that (system integration module) SCIM (single-chip integration module).
NOTE:
EB371 MOTOROLA
Engineering Bulletin
Table System Frequencies from 32.768-kHz Low-Frequency Reference 4.194-MHz High Frequency References 16-MHz Devices
Modulus 000000 000001 000010 000011 000100 000101 000110 000111 001000 001001 001010 001011 001100 001101 001110 001111 010000 010001 010010 010011 010100 010101 010110 010111 011000 011001 011010 011011 [W:X] 1049 1180 1311 1442 1573 1704 1835 1966 2097 2228 2359 2490 2621 2753 2884 3015 3146 3277 3408 3539 3670 Prescaler [W:X] 1049 1311 1573 1835 2097 2359 2621 2884 3146 3408 3670 3932 4194 4456 4719 4981 5243 5505 5767 6029 6291 6554 6816 7078 7340 [W:X] 1049 1573 2097 2621 3146 3670 4194 4719 5243 5767 6291 6816 7340 7864 8389 [W:X] 1049 2097 3146 4194 5243 6291 7340 8389 9437 10486 11534 12583 13631 14680 15729 16777
EB371 MOTOROLA
Engineering Bulletin Introduction
Table System Frequencies from 32.768-kHz Low-Frequency Reference 4.194-MHz High Frequency References 16-MHz Devices (Continued)
Modulus 011100 011101 011110 011111 100000 100001 100010 100011 100100 100101 100110 100111 101000 101001 101010 101011 101100 101101 101110 101111 110000 110001 110010 110011 110100 110101 110110 110111 111000 111001 [W:X] 3801 3932 4063 4194 4325 4456 4588 4719 4850 4981 5112 5243 5374 5505 5636 5767 5898 6029 6160 6291 6423 6554 6685 6816 6947 7078 7209 7340 7471 7602 Prescaler [W:X] 7602 7864 8126 8389 8651 8913 9175 9437 9699 9961 10224 10486 10748 11010 11272 11534 11796 12059 12321 12583 12845 13107 13369 13631 13894 14156 14418 14680 14942 15204 [W:X] [W:X]
EB371 MOTOROLA
Engineering Bulletin
Table System Frequencies from 32.768-kHz Low-Frequency Reference 4.194-MHz High Frequency References 16-MHz Devices (Continued)
Modulus 111010 111011 111100 111101 111110 111111 [W:X] 7733 7864 7995 8126 8258 8389 Prescaler [W:X] 15466 15729 15991 16253 16515 16777 [W:X] [W:X]
Table System Frequencies from 32.768-kHz Low-Frequency Reference 4.194-MHz High-Frequency Reference 20-MHz Devices
Modulus 000000 000001 000010 000011 000100 000101 000110 000111 001000 001001 001010 001011 001100 001101 001110 001111 010000 010001 [W:X] 1049 1180 1311 1442 1573 1704 1835 1966 2097 2228 2359 Prescaler [W:X] 1049 1311 1573 1835 2097 2359 2621 2884 3146 3408 3670 3932 4194 4456 4719 [W:X] 1049 1573 2097 2621 3146 3670 4194 4719 5243 5767 6291 6816 7340 7864 8389 8913 9437 [W:X] 1049 2097 3146 4194 5243 6291 7340 8389 9437 10486 11534 12583 13631 14680 15729 16777 17826 18874 EB371 MOTOROLA
Engineering Bulletin Introduction
Table System Frequencies from 32.768-kHz Low-Frequency Reference 4.194-MHz High-Frequency Reference 20-MHz Devices (Continued)
Modulus 010010 010011 010100 010101 010110 010111 011000 011001 011010 011011 011100 011101 011110 011111 100000 100001 100010 100011 100100 100101 100110 100111 101000 101001 101010 101011 101100 101101 101110 101111 [W:X] 2490 2621 2753 2884 3015 3146 3277 3408 3539 3670 3801 3932 4063 4194 4325 4456 4588 4719 4850 4981 5112 5243 5374 5505 5636 5767 5898 6029 6160 6291 Prescaler [W:X] 4981 5243 5505 5767 6029 6291 6554 6816 7078 7340 7602 7864 8126 8389 8651 8913 9175 9437 9699 9961 10224 10486 10748 11010 11272 11534 11796 12059 12321 12583 [W:X] 9961 10486 [W:X] 19923 20972
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Engineering Bulletin
Table System Frequencies from 32.768-kHz Low-Frequency Reference 4.194-MHz High-Frequency Reference 20-MHz Devices (Continued)
Modulus 110000 110001 110010 110011 110100 110101 110110 110111 111000 111001 111010 111011 111100 111101 111110 111111 [W:X] 6423 6554 6685 6816 6947 7078 7209 7340 7471 7602 7733 7864 7995 8126 8258 8389 Prescaler [W:X] 12845 13107 13369 13631 13894 14156 14418 14680 14942 15204 15466 15729 15991 16253 16515 16777 [W:X] [W:X]
Table System Frequencies from 32.768-kHz Low-Frequency Reference 4.194-MHz High-Frequency Reference 25-MHz Devices
Modulus 000000 000001 000010 000011 000100 000101 000110 000111 [W:X] 1049 Prescaler [W:X] 1049 1311 1573 1835 2097 [W:X] 1049 1573 2097 2621 3146 3670 4194 [W:X] 1049 2097 3146 4194 5243 6291 7340 8389 EB371 MOTOROLA
Engineering Bulletin Introduction
Table System Frequencies from 32.768-kHz Low-Frequency Reference 4.194-MHz High-Frequency Reference 25-MHz Devices (Continued)
Modulus 001000 001001 001010 001011 001100 001101 001110 001111 010000 010001 010010 010011 010100 010101 010110 010111 011000 011001 011010 011011 011100 011101 011110 011111 100000 100001 100010 100011 100100 100101 [W:X] 1180 1311 1442 1573 1704 1835 1966 2097 2228 2359 2490 2621 2753 2884 3015 3146 3277 3408 3539 3670 3801 3932 4063 4194 4325 4456 4588 4719 4850 4981 Prescaler [W:X] 2359 2621 2884 3146 3408 3670 3932 4194 4456 4719 4981 5243 5505 5767 6029 6291 6554 6816 7078 7340 7602 7864 8126 8389 8651 8913 9175 9437 9699 9961 [W:X] 4719 5243 5767 6291 6816 7340 7864 8389 8913 9437 9961 10486 11010 11534 12059 12583 [W:X] 9437 10486 11534 12583 13631 14680 15729 16777 17826 18874 19923 20972 22020 23069 24117 25166
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Engineering Bulletin
Table System Frequencies from 32.768-kHz Low-Frequency Reference 4.194-MHz High-Frequency Reference 25-MHz Devices (Continued)
Modulus 100110 100111 101000 101001 101010 101011 101100 101101 101110 101111 110000 110001 110010 110011 110100 110101 110110 110111 111000 111001 111010 111011 111100 111101 111110 111111 [W:X] 5112 5243 5374 5505 5636 5767 5898 6029 6160 6291 6423 6554 6685 6816 6947 7078 7209 7340 7471 7602 7733 7864 7995 8126 8258 8389 Prescaler [W:X] 10224 10486 10748 11010 11272 11534 11796 12059 12321 12583 12845 13107 13369 13631 13894 14156 14418 14680 14942 15204 15466 15729 15991 16253 16515 16777 [W:X] [W:X]
EB371 MOTOROLA
Engineering Bulletin Introduction
EB371 MOTOROLA
Engineering Bulletin
Motorola reserves right make changes without further notice products herein. Motorola makes warranty, representation guarantee regarding suitability products particular purpose, does Motorola assume liability arising application product circuit, specifically disclaims liability, including without limitation consequential incidental damages. "Typical" parameters which provided Motorola data sheets and/or specifications vary different applications actual performance vary over time. operating parameters, including "Typicals" must validated each customer application customer's technical experts. Motorola does convey license under patent rights rights others. Motorola products designed, intended, authorized components systems intended surgical implant into body, other applications intended support sustain life, other application which failure Motorola product could create situation where personal injury death occur. Should Buyer purchase Motorola products such unintended unauthorized application, Buyer shall indemnify hold Motorola officers, employees, subsidiaries, affiliates, distributors harmless against claims, costs, damages, expenses, reasonable attorney fees arising directly indirectly, claim personal injury death associated with such unintended unauthorized use, even such claim alleges that Motorola negligent regarding design manufacture part. Motorola registered trademarks Motorola, Inc. Motorola, Inc. Equal Opportunity/Affirmative Action Employer.
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