Apple II 11a. Text Mode - cc65/wiki GitHub Wiki

Text mode is the power-on default display mode. To make sure text mode is on you access TXTSET ($C051). The Apple II has 2 text areas. The first, Page 1, is at $0400 and the second, Page 2, is at $0800. Only 1 area is visible at any given time. To select Page 1 access LOWSCR ($C054) and, to select Page 2, access HISCR ($C055).

The Apple II or II+ uses the following set of 64 characters:

@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_ !"#$%&'()*+,-./0123456789:;<=>?

When writing bytes directly into Page 1 or Page 2, this is how this set of 64 characters will be displayed based on the byte written to the display page:

0 - 63 Inverted

64 - 127 Flashing

128 - 191 Normal Set

192 - 255 Normal Set

The Apple //e uses these same characters, but for byte values 224 - 255 it has these additional characters:

`abcdefghijklmnopqrstuvwxyz{|}~░

The text memory has a non-linear organization but it is easy to make a table that will point at the start of each text line. The following assembly code will generate a lo and hi byte table:

rowL:
    .repeat $18, Row
        .byte   ((Row * $80) + (Row / 8 ) * $28) .mod $100
    .endrep

rowH:
    .repeat $18, Row
        .byte   >$0400 | (Row .mod 8 ) / 2
    .endrep

In “C” the table can be generated, or one can simply add code such as this:

const int row[24]= {0x0400, 0x0480, 0x0500, 0x0580, 0x0600, 0x0680, 0x0700, 
0x0780, 0x0428, 0x04A8, 0x0528, 0x05A8, 0x0628, 0x06A8, 0x0728, 0x07A8, 
0x0450, 0x04D0, 0x0550, 0x05D0, 0x0650, 0x06D0, 0x0750, 0x07D0};

To use the row (or rowL/H), look up the line start by the Y position. Add the X position to the looked-up value and that’s the address of the character on the screen at the Y (row) and X (col) location.

Note:

• cc65 will, by default, place Apple II program in the Page 2 memory (at $0803).
• If you want to use Page 2, you can either tell cl65 to use a new start address with the --start-addr option, or you can add a .cfg file to src/apple2 in which you override the start address. Use an address past Page 2’s end. I used $0C00 and that worked great.
• To use the --start-addr with the Makefile, change the $(NAME).apple2: LDFLAGS += for a start address of $0C00 with an all assembly code program to: $(NAME).apple2: LDFLAGS += -u __EXEHDR__ apple2.lib --start-addr 0x0C00 or, for a “C” program, the following (the previous will work but some of it is redundant): $(NAME).apple2: LDFLAGS += --start-addr 0x0C00
• Remember to adjust the row definition (rowH for assembly) from $400 to $800 for Page 2, or add the high-byte on-the-fly if both pages are being used.