HT45FH4M
Lithium Battery Backup Power ASSP MCU
Table Program Example
Theꢀfollowingꢀexampleꢀshowsꢀhowꢀtheꢀtableꢀpointerꢀandꢀtableꢀdataꢀisꢀdefinedꢀandꢀretrievedꢀfromꢀtheꢀ
microcontroller.ꢀThisꢀexampleꢀusesꢀrawꢀtableꢀdataꢀlocatedꢀinꢀtheꢀProgramꢀMemoryꢀwhichꢀisꢀstoredꢀ
thereꢀusingꢀtheꢀORGꢀstatement.ꢀTheꢀvalueꢀatꢀthisꢀORGꢀstatementꢀisꢀ“700H”ꢀwhichꢀrefersꢀtoꢀtheꢀstartꢀ
addressꢀofꢀtheꢀlastꢀpageꢀwithinꢀtheꢀ2KꢀwordsꢀProgramꢀMemoryꢀofꢀtheꢀdevice.ꢀTheꢀtableꢀpointerꢀisꢀ
setupꢀhereꢀtoꢀhaveꢀanꢀinitialꢀvalueꢀofꢀ“06H”.ꢀThisꢀwillꢀensureꢀthatꢀtheꢀfirstꢀdataꢀreadꢀfromꢀtheꢀdataꢀ
tableꢀwillꢀbeꢀatꢀtheꢀProgramꢀMemoryꢀaddressꢀ“706H”ꢀorꢀ6ꢀlocationsꢀafterꢀtheꢀstartꢀofꢀtheꢀlastꢀpage.ꢀ
Noteꢀthatꢀtheꢀvalueꢀforꢀtheꢀtableꢀpointerꢀisꢀreferencedꢀtoꢀtheꢀfirstꢀaddressꢀofꢀtheꢀpresentꢀpageꢀifꢀtheꢀ
“TABRDꢀ[m]”ꢀinstructionꢀisꢀbeingꢀused.ꢀTheꢀhighꢀbyteꢀofꢀtheꢀtableꢀdataꢀwhichꢀinꢀthisꢀcaseꢀisꢀequalꢀ
toꢀzeroꢀwillꢀbeꢀtransferredꢀtoꢀtheꢀTBLHꢀregisterꢀautomaticallyꢀwhenꢀtheꢀ“TABRDꢀ[m]”ꢀinstructionꢀisꢀ
executed.
BecauseꢀtheꢀTBLHꢀregisterꢀisꢀaꢀread-onlyꢀregisterꢀandꢀcannotꢀbeꢀrestored,ꢀcareꢀshouldꢀbeꢀtakenꢀ
toꢀensureꢀitsꢀprotectionꢀifꢀbothꢀtheꢀmainꢀroutineꢀandꢀInterruptꢀServiceꢀRoutineꢀuseꢀtableꢀreadꢀ
instructions.ꢀIfꢀusingꢀtheꢀtableꢀreadꢀinstructions,ꢀtheꢀInterruptꢀServiceꢀRoutinesꢀmayꢀchangeꢀtheꢀ
valueꢀofꢀtheꢀTBLHꢀandꢀsubsequentlyꢀcauseꢀerrorsꢀifꢀusedꢀagainꢀbyꢀtheꢀmainꢀroutine.ꢀAsꢀaꢀruleꢀitꢀisꢀ
recommendedꢀthatꢀsimultaneousꢀuseꢀofꢀtheꢀtableꢀreadꢀinstructionsꢀshouldꢀbeꢀavoided.ꢀHowever,ꢀinꢀ
situationsꢀwhereꢀsimultaneousꢀuseꢀcannotꢀbeꢀavoided,ꢀtheꢀinterruptsꢀshouldꢀbeꢀdisabledꢀpriorꢀtoꢀtheꢀ
executionꢀofꢀanyꢀmainꢀroutineꢀtable-readꢀinstructions.ꢀNoteꢀthatꢀallꢀtableꢀrelatedꢀinstructionsꢀrequireꢀ
twoꢀinstructionꢀcyclesꢀtoꢀcompleteꢀtheirꢀoperation.
Table Read Program Example
tempreg1 db ?
; temporary register #1
tempreg2 db ?
; temporary register #2
:
:
mov a,06h
mov tblp,a
mov a,07h
mov tbhp,a
:
; initialise low table pointer - note that this address is referenced
; initialise high table pointer
:
tabrd tempreg1
; transfers value in table referenced by table pointer data at program
; memory address “706H” transferred to tempreg1 and TBLH
; reduce value of table pointer by one
dec tblp
tabrd tempreg2
; transfers value in table referenced by table pointer data at program
; memory address “705H” transferred to tempreg2 and TBLH in this
; example the data “1AH” is transferred to tempreg1 and data “0FH” to
; register tempreg2
:
:
org 700h
; sets initial address of program memory
dc 00Ah, 00Bh, 00Ch, 00Dh, 00Eh, 00Fh, 01Ah, 01Bh
:
:
Rev. 1.10
19
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HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
