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--- histcomp:apple_ii [2024-09-04 07:09] – asdf
+++ histcomp:apple_ii [2024-10-01 06:15] (current) – asdf
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 The particular revision we have contains a total of 1 MB of RAM.
+===== Sample code =====
+==== Determining current execution page ====
+This snippet is particularly useful for writing peripheral card ROM, where the code needs to function irrespective of its installed slot. It works by calling a "subroutine" consisting entirely of an ''RTS'' (\$FF58 is one of a handful of addresses that Apple guaranteed will contain an ''RTS'' instruction). Upon returning, ''$100+S'' contains the high byte of the return (calling) address.
+If calling from a peripheral card, the slot number can be identified by ANDing the result with 0F.
+<code asm6502>
+; stores the high byte of the execution address in the A register
+; clobbers: A, X
+getpage:
+    JSR $FF58    ; push the return address to the stack
+    TSX          ; use stack pointer as index to stack page
+    LDA $100,X   ; get high byte of return address
+    RTS
+</code>
+==== Writing bytes as hexadecimal ====
+We don't have to reinvent the wheel for this one --- the [[#system monitor]] includes a handy routine called ''PRBYTE'' (\$FDDA) for just this task, shown below [(a2eenhpg)]:
+<code asm6502>
+PRBYTE:    PHA
+           LSR A
+           LSR A
+           LSR A
+           LSR A
+           JSR PRHEXZ    ; =$FDE5
+           PLA
+PRHEX:     AND #$0F
+PRHEXZ:    ORA #$B0
+           CMP #$BA
+           BCC COUT      ; =$FDED
+           ADC #$06
+COUT:      JMP (CSWL)    ; =$0036, user output routine
+</code>
+To make use of it from Applesoft, load the following anywhere into memory:
+<code asm6502>
+JSR $DEBE      ; CHKCOM - skips comma in Applesoft parsing
+JSR $DFE3      ; GETPNT - get pointer to variable data, put it in $83...$84
+LDY #$00
+LDA ($83),Y    ; get high byte from VARPNT
+JSR $FDDA      ; PRBYTE
+INY
+LDA ($83),Y    ; get low byte from VARPNT
+JMP $FDDA      ; PRBYTE (will RTS for us)
+</code>
+Then it can be called from Applesoft like so (assuming the program was loaded at \$0300):
+<code basic>
+LET X% = 69
+CALL 768,X%
+</code>
+==== Generate the Mandelbrot set ====
+Useful as a benchmark. The computer must be in 80-column mode for it to display properly.
+<code basic>
+FOR Y=-12 TO 12
+FOR X=-39 TO 39
+CA=X*0.0458
+CB=Y*.08333
+A=CA
+B=CB
+FOR I = 0 TO 15
+T=A*A-B*B+CA
+B=2*A*B+CB
+A=T
+IF(A*A+B*B)>4 GOTO 200
+NEXT I
+PRINT " ";
+GOTO 210
+IF I>9 THEN I=I+7
+PRINT CHR$(48+I);
+NEXT X
+PRINT
+NEXT Y
+</code>
 ===== Resources =====
@@ Line 233: / Line 312: @@
 [(a2etechrefmanual>[[https://mirrors.apple2.org.za/Apple%20II%20Documentation%20Project/Computers/Apple%20II/Apple%20IIe/Manuals/Apple%20IIe%20Technical%20Reference%20Manual.pdf|Apple IIe Technical Reference Manual]])]
 [(msc80scschem>https://mirrors.apple2.org.za/Apple%20II%20Documentation%20Project/Interface%20Cards/Z80%20Cards/Microsoft%20SoftCard/Schematics/)]
+[(a2eenhpg>[[https://ia804504.us.archive.org/19/items/about-your-enhanced-apple-iie-programmers-guide/About%20Your%20Enhanced%20Apple%20IIe%20Programmer%27s%20Guide.pdf|About Your Enhanced Apple IIe: Programmer's Guide]])]
+[(Sather1985>[[https://ia800702.us.archive.org/18/items/Understanding_the_Apple_IIe/Understanding_the_Apple_IIe.pdf|Understanding the Apple IIe]] (1985))]
+[(usingprodos>[[https://mirrors.apple2.org.za/ftp.apple.asimov.net/documentation/os/prodos/Using%20ProDOS%20-%20The%20Multilayered%20DOS.pdf|Using ProDOS]])]
+[(allpinoutsa2>[[https://allpinouts.org/pinouts/connectors/buses/apple-ii-slot/]])]
 ~~REFNOTES~~