65c02 Assembly programming for the Apple IIe

The Apple II saw many generations of it's hardware, from the early Apple II to the final Apple IIgs the hardware remained mostly compatible, however the harfdware was heavily upgraded, moving from a 4k 6502, to a 8mb 16 bit 65816

The most curious thing from our point of view is that the Apple II used 3 generations of the 6502, and it's the Apple IIe with its enhanced 8 bit 65C02 we'll cover in these tutorials
There are many versions of the Apple 2, we're only going to cover the Apple IIe in these tutorials.
Apple II Apple IIe Apple IIgs
Cpu 1mhz 6502
1mhz 65C02 2mhz 65C816 (16 bit)
Ram 4k  48k up to 8mb
Resolution Text Only 280×192 320x200
Sound beeper beeper Ensonique 5503

Apple IIe Memory Map
The Apple IIc memory map is pretty typical.

We'll use Graphics Mode, and Page 2 - this means for our purposes the area $0C00-$3FFF can be used for our main program code.

Notice that the area $C000-$FFFF allows us to access the hardware...

Each "Port" has a different purpose, but rather strangely  when we want to do something like set the graphics mode, we write ANY value to the graphics port... the value makes no difference!
From To Purpose
$0000 $00FF Zero page
$0100 $01FF Stack
$0200 $02FF GETLN buffer
$0300 $03CF Free Space
$03D0 $03FF DOS & Interrupt vectors
$0400 $07FF Text Screen Page 1
$0800 $0BFF Text Screen Page 2
$0C00 $1FFF Free space
$2000 $3FFF Graphics Screen Page 1
$4000 $5FFF Graphics Screen Page 2
$6000 $95FF Applesoft String Data
$9600 $BFFF Operating System Memory
$C000 $FFFF System Harware ports

Hardware Ports Memory Map
Writing any value to these memory addreses causes the hardware change.

For example, to change the system to graphics mode:

    lda #0
    sta $C050 ; Text off
    sta $C052 ; Mixed Mode off
    sta $c057  ; Display hires
    sta $C055 ; Hires screen 2
       
Reading from the ports will also have the same effect!
Address Code Details
C050 TXTCLR Display Graphics
C051 TXTSET Display Text
C052 MIXCLR Display Full Screen
C053 MIXSET Display Split Screen
C054 TXTPAGE1 Display Page 1
C055 TXTPAGE2 Display Page 2
C056 LORES Display LoRes Graphics
C057 HIRES Display HiRes Graphics

Highres Screen - Screen Colors
Colors on the Apple II are effectively an 'Artifact' of the screen...

certain combinations of Off (0) and On (1) pixels will appear colored... this is known as Composite Artifact colors...

Unlike pretty much every system in existance, 8 bits of a byte draw 7 pixels!.... the top bit is a 'Color bit'... selecting 'Palette 0 or 1

The remaining 7 bits are the 7 pixels of bitmap data... because each line is 40 bytes wide, the Apple II screen is a rather odd resolution of 280×192
Bitnum 7 6 5 4 3 2 1 0
Function  Color   Pixel 1   Pixel 2   Pixel 3   Pixel 4   Pixel 5   Pixel 6   Pixel 7 


Pixel Pair
Color Bit   00     01     10     11  
0 00
01
10
11
1 00
01
10
11
Because of these artifacts, a '2 color' bitmap will show colors depending on the combination of the pixels...

My Akusprite editor offers a half horizontal resolution mode, where the 4 colors will be converted to the correct bit combinations
Normal Pixel data - 2 color Half Horizontal resolution - 4 color


Highres Screen Mode 2 - Memory map
Memory addresses for Screen Mode 2 is split into 3 chunks,also, every 8 lines we effectively 'reset' our high memory address and add $80

1st Third

Lines 0-63
2nd Third

Lines 64-127
3rd Third

Lines 128-191

Pixels in Each line are in normal Left->Right format, however remeber 7 pixels are defined by each byte, with 1 bit defining the color palette.

We can calculate the address of the start of a line by splitting the bits of the Y line number...

YPOS:
 7  6  5  4  3  2  1  0
A A B B B C C C

Address= Base+(AA*$0028) + (BBB*$0080) + (CC*$0400) + XPOS



1st Third
Lines 0-63
2nd Third
Lines 64-127
3rd Third
Lines 128-191
Unused
0 $4000-$4027 $4028-$404F $4050-$4077 $4078-$407F
1 $4400-$4427 $4428-$444F $4450-$4477 $4478-$447F
2 $4800-$4827 $4828-$484F $4850-$4877 $4878-$487F
3 $4C00-$4C27 $4C28-$4C4F $4C50-$4C77 $4C78-$4C7F
4 $5000-$5027 $5028-$504F $5050-$5077 $5078-$507F
5 $5400-$5427 $5428-$544F $5450-$5477 $5478-$547F
6 $5800-$5827 $5828-$584F $5850-$5877 $5878-$587F
7 $5C00-$5C27 $5C28-$5C4F $5C50-$5C77 $5C78-$5C7F
8 $4080-$40A7 $40A8-$40CF $40D0-$40F7 $40F8-$40FF
9 $4480-$44A7 $44A8-$44CF $44D0-$44F7 $44F8-$44FF
10 $4880-$48A7 $48A8-$48CF $48D0-$48F7 $48F8-$48FF
11 $4C80-$4CA7 $4CA8-$4CCF $4CD0-$4CF7 $4CF8-$4CFF
12 $5080-$50A7 $50A8-$50CF $50D0-$50F7 $50F8-$50FF
13 $5480-$54A7 $54A8-$54CF $54D0-$54F7 $54F8-$54FF
14 $5880-$58A7 $58A8-$58CF $58D0-$58F7 $58F8-$58FF
15 $5C80-$5CA7 $5CA8-$5CCF $5CD0-$5CF7 $5CF8-$5CFF
16 $4100-$4127 $4128-$414F $4150-$4177 $4178-$417F
17 $4500-$4527 $4528-$454F $4550-$4577 $4578-$457F
18 $4900-$4927 $4928-$494F $4950-$4977 $4978-$497F
19 $4D00-$4D27 $4D28-$4D4F $4D50-$4D77 $4D78-$4D7F
20 $5100-$5127 $5128-$514F $5150-$5177 $5178-$517F
21 $5500-$5527 $5528-$554F $5550-$5577 $5578-$557F
22 $5900-$5927 $5928-$594F $5950-$5977 $5978-$597F
23 $5D00-$5D27 $5D28-$5D4F $5D50-$5D77 $5D78-$5D7F
24 $4180-$41A7 $41A8-$41CF $41D0-$41F7 $41F8-$41FF
25 $4580-$45A7 $45A8-$45CF $45D0-$45F7 $45F8-$45FF
26 $4980-$49A7 $49A8-$49CF $49D0-$49F7 $49F8-$49FF
27 $4D80-$4DA7 $4DA8-$4DCF $4DD0-$4DF7 $4DF8-$4DFF
28 $5180-$51A7 $51A8-$51CF $51D0-$51F7 $51F8-$51FF
29 $5580-$55A7 $55A8-$55CF $55D0-$55F7 $55F8-$55FF
30 $5980-$59A7 $59A8-$59CF $59D0-$59F7 $59F8-$59FF
31 $5D80-$5DA7 $5DA8-$5DCF $5DD0-$5DF7 $5DF8-$5DFF
32 $4200-$4227 $4228-$424F $4250-$4277 $4278-$427F
33 $4600-$4627 $4628-$464F $4650-$4677 $4678-$467F
34 $4A00-$4A27 $4A28-$4A4F $4A50-$4A77 $4A78-$4A7F
35 $4E00-$4E27 $4E28-$4E4F $4E50-$4E77 $4E78-$4E7F
36 $5200-$5227 $5228-$524F $5250-$5277 $5278-$527F
37 $5600-$5627 $5628-$564F $5650-$5677 $5678-$567F
38 $5A00-$5A27 $5A28-$5A4F $5A50-$5A77 $5A78-$5A7F
39 $5E00-$5E27 $5E28-$5E4F $5E50-$5E77 $5E78-$5E7F
40 $4280-$42A7 $42A8-$42CF $42D0-$42F7 $42F8-$42FF
41 $4680-$46A7 $46A8-$46CF $46D0-$46F7 $46F8-$46FF
42 $4A80-$4AA7 $4AA8-$4ACF $4AD0-$4AF7 $4AF8-$4AFF
43 $4E80-$4EA7 $4EA8-$4ECF $4ED0-$4EF7 $4EF8-$4EFF
44 $5280-$52A7 $52A8-$52CF $52D0-$52F7 $52F8-$52FF
45 $5680-$56A7 $56A8-$56CF $56D0-$56F7 $56F8-$56FF
46 $5A80-$5AA7 $5AA8-$5ACF $5AD0-$5AF7 $5AF8-$5AFF
47 $5E80-$5EA7 $5EA8-$5ECF $5ED0-$5EF7 $5EF8-$5EFF
48 $4300-$4327 $4328-$434F $4350-$4377 $4378-$437F
49 $4700-$4727 $4728-$474F $4750-$4777 $4778-$477F
50 $4B00-$4B27 $4B28-$4B4F $4B50-$4B77 $4B78-$4B7F
51 $4F00-$4F27 $4F28-$4F4F $4F50-$4F77 $4F78-$4F7F
52 $5300-$5327 $5328-$534F $5350-$5377 $5378-$537F
53 $5700-$5727 $5728-$574F $5750-$5777 $5778-$577F
54 $5B00-$5B27 $5B28-$5B4F $5B50-$5B77 $5B78-$5B7F
55 $5F00-$5F27 $5F28-$5F4F $5F50-$5F77 $5F78-$5F7F
56 $4380-$43A7 $43A8-$43CF $43D0-$43F7 $43F8-$43FF
57 $4780-$47A7 $47A8-$47CF $47D0-$47F7 $47F8-$47FF
58 $4B80-$4BA7 $4BA8-$4BCF $4BD0-$4BF7 $4BF8-$4BFF
59 $4F80-$4FA7 $4FA8-$4FCF $4FD0-$4FF7 $4FF8-$4FFF
60 $5380-$53A7 $53A8-$53CF $53D0-$53F7 $53F8-$53FF
61 $5780-$57A7 $57A8-$57CF $57D0-$57F7 $57F8-$57FF
62 $5B80-$5BA7 $5BA8-$5BCF $5BD0-$5BF7 $5BF8-$5BFF
63 $5F80-$5FA7 $5FA8-$5FCF $5FD0-$5FF7 $5FF8-$5FFF


Learn Assembly for the Greatest Classic Processors:  Z80 - 6502 - 68000
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