Holtek BS82B12A-3 - Reset and Initialisation

Rev. 1.20 58 January 23, 2015 Rev. 1.20 59 January 23, 2015
BS82B12A-3/BS82C16A-3/BS82D20A-3
Touch Key 8-Bit Flash MCU with LED/LCD Driver
BS82B12A-3/BS82C16A-3/BS82D20A-3
Touch Key 8-Bit Flash MCU with LED/LCD Driver
000:2
8
/f
SUB
WS[2:0]=
f
SUB
CLR
Reset
MCU
11 stage divider
8-to-1 MUX
WDT Time-out
WS2~WS0
7-stage Divider
(f SUB /2
1
~f SUB /2
11
)
001:2
10
/f
SUB
010:2
12
/f SUB
011:2
14
/f SUB
100:2
15
/f SUB
101:2
16
/f SUB
110:2
17
/f SUB
111:2
18
/f SUB
“HALT”Instruction
“CLR WDT”Instruction
WE4~WE0 bitsWDTC Register
LIRC
LXT
M
U
X
Configuration
Option
Note:FortheBS82B12A-3device,thef
SUB
issuppliedonlybytheLIRCoscillator.
Watchdog Timer
Reset and Initialisation
Aresetfunctionisafundamentalpartofanymicrocontrollerensuringthatthedevicecanbeset
tosomepredeterminedconditionirrespectiveofoutsideparameters.Themostimportantreset
conditionisafterpowerisrstappliedtothemicrocontroller.Inthiscase,internalcircuitrywill
ensurethatthemicrocontroller,afterashortdelay,willbeinawelldefinedstateandreadyto
executetherstprograminstruction.Afterthispower-onreset,certainimportantinternalregisters
willbesettodenedstatesbeforetheprogramcommences.OneoftheseregistersistheProgram
Counter,whichwillberesettozeroforcingthemicrocontrollertobeginprogramexecutionfromthe
lowestProgramMemoryaddress.
AnothertypeofresetiswhentheWatchdogTimeroverflowsandresetsthemicrocontroller.All
typesofresetoperationsresultindifferentregisterconditionsbeingsetup.Anotherresetexistsinthe
formofaLowVoltageReset,LVR,whereafullreset,isimplementedinsituationswherethepower
supplyvoltagefallsbelowacertainthreshold.
Reset Functions
Thereareseveralwaysinwhichamicrocontrollerresetcanoccur,througheventsoccurringinternally:
Power-on Reset
Themostfundamentalandunavoidableresetistheonethatoccursafterpowerisrstappliedto
themicrocontroller.AswellasensuringthattheProgramMemorybeginsexecutionfromtherst
memoryaddress,apower-onresetalsoensuresthatcertainotherregistersarepresettoknown
conditions.AlltheI/Oportandportcontrolregisterswillpowerupinahighconditionensuringthat
allpinswillberstsettoinputs.
VDD
Power-on
Reset
SST Time-out
t
RSTD
Note:t
RSTD
ispower-ondelay,typicaltime=50ms
Power-On Reset Timing Chart