Mountain Computer ROMPlus+ Operating Manual

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Chapter 3ADVANCED PROGRAMMERS INFORMATIONWriting Your Own ROMThere are a few things you should remember when writing your ownROMs. First, your program should never reference location $CFFF.Any reference to that address will disable all memory that mapsinto $C800-$CFFF. If you do reference that address, you willdisable ROMPLUS+.The slot number of ROMPLUS+ may be found by your program byreading $7F8. It will contain the value $CN where N is the slotnumber. Location $6F8+N contains the value $NO.The control ROM makes sure that RAM is active whenever a ROMsocket is selected. If your program must deactivate the RAM, itmust reactivate RAM before it finishes executing.Programs On Two ROMsThe 2K bytes of storage on each ROM is large enough for all butthe larger programs. If you have an application program that islarger than 2K bytes, there is a scheme allowing you to use twoROMs in conjunction.ROMPLUS+ will map anyone of the six ROMs into the $C800-$CFFFaddress space at one time~ If you simply had the first ROM writea con t r 0 1 w 0 r d w h.i c h s wit c h est heR OMs 0 c k e t n u m be r tot hen e wROM socket number, your program will immediately swi tch to theother ROM. This usually blows up the program.One solution to this problem is to write a subroutine dispatchingsubroutine, and place this subroutine into identical addresses onthe two ROMs. This way, you enter the subroutine dispatchingsubroutine on the first ROM, the switching of ROM occurs, and thedispatching routine continues on the second ROM, because theidentical addresses contain identical code.Here is the code which will do the task:*The A register contains the ROM socket number*you wish to use. The Y register contains a*value which determines which routine is run (routine*number *2). You must preserve the X register.MSLOTCONTROLCHIPNUMSUBADDREQUEQUEQUEQU$7F8$C080$0$13-6
Chapter 3ADVANCED PROGRAMMERS INFORMATIONCHIPCALLSTALDXLDATAXLDAORAPHAANDORASTACHIPNUMMSLOT$638,XCONTROL,X11$08II$F8CHIPNUMCONTROL,XAt this point, we are now on the other ROM.specified by Y.CALLSUBSUBTABLELDASTALDASTAJSRPLASTARTSJMPDADAIt is necessary for thisaddresses on the two ROMs.may be located anywherepossible memory conflicts.of $1 and $2.SUBTABLE,XSUBADDRSUBTABLE+1,ySUBADDR+1CALLSUBCONTROL,X(SUBADDR)SUB1StJB2:save ROM number:get $CN:get $NO:x contains value $NO:get control word:turn on activate bit 3:save so we can restorelater:set ROM number to zero:or in new ROM number:write to control wordCall routine:get low byte of address:and store here:get high byte of address:and store here:indirect subroutine call:return, get old state:restore old ROM:return out of this routine:indirect jump to routine:table of routine addresses:low byte first, high bytesecondroutine to be located at identicalOtherwise it will not work~-SUBADDRin memory as long as there are noWe recommend the page zero addressesThe program "CHIPCALLw is a subroutine, and should be called withthe "JSR" instruction. Before you call the subroutine, set upthe "A" and "Y" registers. The value of the X register must bepreserved.3-7
Page 3 and 4: Table of ContentsiiiChapter 1INTROD
Page 5: INST ALL A TIONTo install ROMPLUS+
Page 9 and 10: Chapter 2USING ROMPLUS+This chapter
Page 11 and 12: Chapter 2USING ROMPLUS+CTRL-SHIFT-M
Page 13 and 14: Chapter 3ADVANCED PROGRAMMER'S INFO
Page 15 and 16: Chapter 3ADVANCED PROGRAMMERS INFOR
Page 17: Chapter 3ADVANCED PROGRAMMERS INFOR
Page 21: Chapter 4REFERENCEa ROM socket. ROM
Page 24 and 25: Appendix ACONTROL ROM SOURCE LISTIN
Page 26 and 27: Appendix ACONTROL ROM SOURCE LISTIN
Page 28: Appendix ACONTROL ROM SOURCE LISTIN

Mountain Computer ROMPlus+ Operating Manual

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