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 hardware 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

ChibiAkumas Tutorials

Useful Documents
understanding_the_apple_ii - Great breakdown of the Apple II hardware
Understanding_the_Apple_IIe - Apple IIe version!
Port Map - Apple II ports

Useful Tools
CiderPress - Disk editor

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

Analog Joystick

On the Apple 2, we'll be using Analog Joysticks... these return a value for the X and Y axis in a range of 0-100 0,0 is Top,Left.... 100,100 is Bottom,Right We're going to read these in and convert them to Digital Values

There are several ports we need to know about on the Apple II Reading Analogs on the Apple II is a pain... we reset the analogs with $C070, then count up until bit 0 of $C064 (or one of the other analogs) becomes 1 - this value in our count is the analog position In thory the Apple II as 4 switches (0-3) but we can only easily use 0 and 1 Each Joystick will use Two Analogs, 0 & 1 for Joystick 1, and 2 & 3 for Joystick 2 Port Name Details Notes $C060  BUTN3 Switch Input 3 Bit 7=0 when Down $C061 RDBTN0  Switch Input 0 / Open Apple  Bit 7=0 when Down $C062 BUTN1 Switch Input 1 / Solid Apple Bit 7=0 when Down $C063 RD63 Switch Input 2 / Shift Key Bit 7=0 when Down $C064 PADDL0 Analog Input 0 Bit 7=0 when Count reached  $C065 PADDL1 Analog Input 1 Bit 7=0 when Count reached $C066 PADDL2 Analog Input 2 Bit 7=0 when Count reached $C067 PADDL3 Analog Input 3 Bit 7=0 when Count reached $C070 PTRIG Analog Input Reset Reset Analog Count