HT67F5652 datasheet(160/224 Pages) HOLTEK

160 / 224 page

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HT67F5652

24-Bit Delta Sigma A/D + LCD Flash MCU

HT67F5652

24-Bit Delta Sigma A/D + LCD Flash MCU

Baud Rate Generator

Tosetupthespeedoftheserialdatacommunication,theUARTfunctioncontainsitsowndedicated

baudrategenerator.Thebaudrateiscontrolledbyitsowninternalfreerunning8-bittimer,the

periodofwhichisdeterminedbytwofactors.Thefirstoftheseisthevalueplacedinthebaudrate

registerBRGandthesecondisthevalueoftheBRGHbitwiththecontrolregisterUCR2.The

BRGHbitdecidesifthebaudrategeneratoristobeusedinahighspeedmodeorlowspeedmode,

whichinturndeterminestheformulathatisusedtocalculatethebaudrate.ThevalueNintheBRG

registerwhichisusedinthefollowingbaudratecalculationformuladeterminesthedivisionfactor.

NotethatNisthedecimalvalueplacedintheBRGregisterandhasarangeofbetween0and255.

UCR2 BRGH Bit

Baud Rate (BR)

fSYS / [�4 (N+1)]

fSYS / [1� (N+1)]

ByprogrammingtheBRGHbitwhichallowsselectionoftherelatedformulaandprogrammingthe

requiredvalueintheBRGregister,therequiredbaudratecanbesetup.Notethatbecausetheactual

baudrateisdeterminedusingadiscretevalue,N,placedintheBRGregister,therewillbeanerror

associatedbetweentheactualandrequestedvalue.ThefollowingexampleshowshowtheBRG

registervalueNandtheerrorvaluecanbecalculated.

Calculating the Register and Error Values

Foraclockfrequencyof4MHz,andwithBRGHclearedtozerodeterminetheBRGregistervalueN,

theactualbaudrateandtheerrorvalueforadesiredbaudrateof4800.

FromtheabovetablethedesiredbaudrateBR=fSYS/[64(N+1)]

Re-arrangingthisequationgivesN=[fSYS/(BR×64)]-1

GivingavalueforN=[4000000/(4800×64)]-1=12.0208

Toobtaintheclosestvalue,adecimalvalueof12shouldbeplacedintotheBRGregister.Thisgives

anactualorcalculatedbaudratevalueofBR=4000000/[64×(12+1)]=4808

Thereforetheerrorisequalto(4808-4800)/4800=0.16%

ThefollowingtablesshowactualvaluesofbaudrateanderrorvaluesforthetwovaluesofBRGH.

Baud

Rate

K/BPS

Baud Rates for BRGH=0

fSYS=4MHz

fSYS=3.579545MHz

fSYS=7.159MHz

BRG

Kbaud Error (%) BRG

Kbaud Error (%) BRG Kbaud Error (%)

0.3

�0�

0.300

0.1�

185

0.300

0.00

—

1.�

1.�0�

0.1�

4�

1.190

-0.83

9�

1.�03

0.�3

�.4

�5

�.404

0.1�

��

�.43�

1.3�

4�

�.380

-0.83

4.8

1�

4.808

0.1�

4.��1

-�.90

��

4.8�3

1.3�

9.�

�

8.9�9

-�.99

9.3�1

-�.90

9.33�

-�.90

19.�

�

�0.833

8.51

�

18.�43

-�.90

18.�43

-�.90

38.4

—

�

3�.�8�

-�.90

5�.�

��.500

8.51

55.930

-�.90

55.930

-�.90

115.�

—

111.859

-�.90

Baud Rates and Error Values for BRGH = 0

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