Apple-1 character mapping is incorrect for the lowercase ASCII range #47
Description
If you run the Apple-1 character test program from the user's manual
0: A9 0 AA 20 EF FF E8 8A 4C 2 0
0R
you should get output similar to the following:
If you closely inspect the output and compare it to the output from Apple 1js https://www.scullinsteel.com/apple1/:
you'll notice that the OpenEmulator character mapping for lowercase ASCII is incorrect.
The correctness of the Apple 1js output can be confirmed by checking any image from a real Apple-1, e.g. (you'll need to zoom in on this one):
Note: When mapping 7-bit ASCII display characters to the 6-bit Signetics 2513 character index, the Apple-1 drops ASCII bit 5 (0x20) and concatenates a negated bit 6 (0x40) with bits [4:0] to form the 2513 6-bit input.
| ASCII Range | Remapped value | 2513 (6-bit) character | Note |
|---|---|---|---|
| 0x00-0x1F control chars | 0x20-0x3F | 0x20-0x3F symbols | Not displayed, all but CR ignored |
| 0x20-0x3F symbols | 0x20-0x3F | 0x20-0x3F symbols | |
| 0x40-0x5F uppercase | 0x00-0x1F | 0x00-0x1F uppercase | |
| 0x60-0x7E lowercase | 0x00-0x1F | 0x00-0x1F uppercase |