screenshots
Here we’ve configured an Apple ][ plus, with a disk controller in slot 6, and a language card in slot 0. We’ve booted the DOS 3.3 System Master disk. It correctly identifies the machine as an Apple ][ plus, and then loads Integer BASIC into the language card. You can switch between Applesoft and Integer BASIC by using the FP and INT commands.
Here we’ve configured an Apple ][ (Integer BASIC ROMs), with a Revision Zero motherboard, and a disk controller (with 13-sector ROMs) in slot 6. With a revision 0 motherboard, when the machine is powered-on, the CPU doesn’t start actually running until you manually press the RESET button. Also, the old Monitor ROMs do not boot from the disk drives automatically; you need to type C600G to boot. We’ve booted the DOS 3.1 System Master disk and done a catalog of it. As you can see, with a revision 0 motherboard, the text is displayed in green and purple, which are also the only two HIRES colors. Later revisions of the motherboard added a ``color burst killer'' which is active during text mode, so the text would be strictly white. Two more HIRES colors, blue and orange, were also added in later revisions.
Here we’ve configured an Apple ][ plus with language card and disk drive. We’re booting a PRODOS 1.1.1 disk.
The October 1982 issue of Softalk featured an article by Bob Bishop entitled Have an Apple Split, which describes in some detail the inner workings of the Apple ]['s video processing. Listings 1 and 2 from that article show a short Applesoft program and assembly language subroutine that allow the Apple ][ to have a screen split between text and graphics display. To achieve this on the EPPLE ][, copy the following text and paste it into the emulator (at the Applesoft ] prompt). Since the EPPLE ][ accurately emulates the video scanning and timing of the original Apple ][s, this ``split screen'' technique works successfully. The rest of the behavior described in the article (the floating data bus) is also emulated faithfully by the EPPLE ][.
CALL -151
300:8D 52 C0 A9 E0 A2 04 CD 51 C0 D0 F9 CA D0 F8 A9
310:A0 A2 04 CD 50 C0 D0 F9 CA D0 F8 8D 51 C0 60
E000G
100 HOME
200 FOR K = 0 TO 39
210 POKE 1448+K, 14*16
220 POKE 2000+K, 10*16
230 COLOR = K+4
240 VLIN 24, 45 AT K
250 NEXT K
300 VTAB 6 : HTAB 17
310 PRINT "APPLE II"
400 CALL 768
500 GOTO 400
RUN
Jim Sather’s book Understanding the Apple II, which was the primary reference for the internal design of the EPPLE ][ emulator, describes the video generation process of the Apple ][, in great detail, in Chapter 8. On page 8-21 he shows a simple Applesoft BASIC program (shown below) that shows an example of one of the hi-res idiosyncrasies on the Apple ][. The program would logically draw three orange lines, but due to the video cutoff and extension of half-dot shifted pixels, instead the right line is brown, and there is a ``mysterious pink line'' (actually magenta) on the far left of the screen. The EPPLE ][ faithfully emulates this behavior.
NEW
10 HGR : HCOLOR = 5 : HPLOT 5,159 TO 5,0 TO 279,0 TO 279,159
RUN
Jim Sather’s book Understanding the Apple II, shows an Applesoft BASIC program and assembly language subroutine on pages 3-16 and 3-17 (reproduced below) that produce the display shown here. The screen is split between HIRES and LORES graphics by a timed loop that manipulates the screen switches. (Press any key repeatedly to move the position of the split.)
Notice that the Apple ][ can actually produce more HIRES colors than are documented in the standard Apple reference manuals. White, black, green, purple, blue, and orange are normally documented, but by careful manipulation of the high-bit (half-dot shift indicator) of the HIRES display byte, many other colors can be produced. The additional colors match some LORES colors. Also notice that the text at the bottom of the screen is colored green and purple while in mixed text/graphics mode. This is because the ``color burst killer'' circuit is not active while displaying graphics on the Apple ][ machines.
CALL -151
1F00:AC 54 C0 A0 27 20 27 1F
1F08:AC 10 C0 AC 00 C0 30 F3
1F10:69 01 29 01 AA BC 56 C0
1F18:A2 08 20 31 1F A0 31 20
1F20:27 1F 18 90 E6 D0 01 88
1F28:88 EA D0 F9 60 48 68 EA
1F30:EA A0 62 20 27 1F EA CA
1F38:D0 F3 60
E000G
30 HGR : HOME : VTAB 21 : PRINT "1 7 D 2 8 E B 4 5 A 3 6 C 9 F 8"
40 DIM COLR(39), X(21)
100 FOR A = 0 TO 39 : READ COLR(A) : COLOR = COLR(A) : VLIN 0, 39 AT A : NEXT A
200 FOR A = 0 TO 21 : READ COLR(A) : READ X(A) : HCOLOR = COLR(A)
210 HPLOT X(A), 0 TO X(A), 159 : NEXT A
220 FOR A = 8319 TO 16383 STEP 128 : POKE A, 64 : NEXT A
300 CALL 7936
400 REM LORES DATA
410 DATA 1,0,7,7,0,13,13,0,2,2,0,8,8,0,14,14,0,11,11,0
420 DATA 4,4,0,0,5,0,0,10,0,3,0,6,0,12,0,9,0,15,0,8
500 REM HIRES DATA
510 DATA 4,0,3,20,4,21,3,41,4,42,7,62,7,83,7,104,3,105,7,125,3,126,7,159,3,161
520 DATA 7,180,3,182,3,206,7,220,3,233,7,247,3,262,3,263,7,279
RUN