Mountain Computer ROMPlus+ Operating Manual

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Chapter 2USING ROMPLUS+A program executed by the CTRL-SHIFT-N command in one ROM mayexecute another ROMPLUS+ program in another ROM by outputtinganothr CTRL-SHIFT-N command. However, a program executed by theCTRL-SHIFT-N command may not output a CTRL-SHIFT-M command. Inthe former case, the control ROM keeps track of control. In thelater case, the control ROM keeps track of control. In the latercase, we have a situation which is logically meaningless. Itdoes not make sense to have a routine type of program calling aspecial driver type program.It does make sense however, to have a driver type program(activated by CTRL-SHIFT-M) call upon a routine type program(CTRL-SHIFT-N). For example, a program such as Keyboard Filtermight call upon a routine on another ROM. It would output aCTRL-SHIFT-N command. The control ROM keeps track of the ca11ingROM and the called ROM. It returns control to the calling ROMwhen the called ROM returns.Selecting RAMAny time ROMPLUS+ is activated, or any ROM is activated via theCTRL-SHIFT-M or CTRL-SHIFT-N commands, the on-board RAM isactivated. Whenever this RAM is active, the top 256 bytes of theselected ROM are not available. If your program uses the top 256bytes of the ROM, you must deactivate the RAM before the code isexecuted. Otherwise, the computer will read the contents of RAMand interpret that data as instructions. This usually results indisaster. It is necessary to reactivate RAM before returningcontrol. The next chapter contains a few rout ines used for controllingthe state of the RAM.NotesThe control ROM on ROMPLUS+ makes use of two locations in memorynormally used by the monitor. These two locations are $3A and$3B. As a result, whenever ROMPLUS+ is active, the monitor "L"command for disassembly and the Apple II mini~assembler will notwork properly. To restore these commands, deactivate ROMPLUS+.The Apple II peripheral scheme states that all ROM's in the$C800-$CFFF space must be de-selected whenever $CFFF isreferenced. Therefore, take care that your programs neverreference location $CFFF.2-4
Chapter 3ADVANCED PROGRAMMER'S INFORMATIONThis chapter contains information for the advanced use ofROMPLUS+. The sections about the control word and the controlROM should be read by anyone using ROMPLUS+. The other sectionsabout the branch table, preparing your ROM, and programs greaterthan 2K bytes are intended for the user that will prepare theirown ROM chip for use in ROMPLUS+. However, anyone using ROMPLUS+will benefit from the information in those sections.The Control WordThe features of ROMPLUS+ are controlled by the control word. Thecontrol word is a read/write word located at a slot dependentmemory address. The address of the control ~ord is $C080+$NO (or-16256+l6*N from BASIC), where N is equal to the slot number.The following table summarizes:Slot II Hex Address BASIC Address---1 $C090 -162402 $COAO -162243 $COBO -162084 $COCO -161925 $CODO -161766 $COEO -161607 $COFO -16144A write to the controlsocket, activate ordeactivate the RAM.described below:word location may be used to select a ROMdeactivate the board, or activate orThe function of the particular bits arecontrol wordBit 7:Bit 6-4:Bit 3:This bit controls the RAM. If a "0" is written,the RAM is deactivated. If a "1" is written,the RAM is activated.Unused.This bi t controls the board. If a "0" iswritten, the ROMPLUS+ is deactivated. If a "1"is written, the board is activated.3-1
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: Chapter 2USING ROMPLUS+CTRL-SHIFT-M
Page 15 and 16: 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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