Keyboard and Character Map
From Maze
Keyboard and Character Map, Hardware and Software
800 × 267 pixels
As we will see when exploring visual alternatives below, the PETSCII CHR table contains few related graphical characters the are next to each other and can be easily addressed by offsets -- in fact, many related images (sets of corners, mirror images) appear to have been randomly scattered through the space. This lack of adjacency complicates our ability to generate graphics using a simple offset -- in fact, to use anything but an offset of one, we have to cast the random number generator's float result to an int before multiplying.
380 × 270 pixels
Why is the order of graphical characters in the PETSCII table so haphazard? The answer is that arrangement was dictated, not by logically grouping index numbers (a program-up strategy), but by arranging them visually on the PET keyboard design (a hardware-down strategy). Because the PET 2001 keyboard was a chicklet variant of the QWERTY arrangement, yet lacking the row offsets that QWERTY designer Christopher Sholes originally created for mechanical typewriter levers, its grid of keys presented a clear canvas for logical groupings of related symbols. Thus we can see four corners of a square grouped on OPL:, four arcs of a circle on UIJK, and four suits of a card deck on ASZX.
This visual logical grouping, however, occurs in the space of the QWERTY keyboard arrangement, which originally attempted to minimize mechanical jams in typewriters by maximizing the distance between common letter pairs. As a side-effect of this principle, few adjacent letters pairs in the alphabetic sequence are actually visual neighbors on the QWERTY keyboard. Other related graphical characters, while adjacent on the physical keyboard, are effectively scrambled by the QWERTY layout before being placed in the alphabetized PETSCII index. This preserves their logical relationship to the keys (any graphical character can be transformed into its letter, or vice-versa, by a fixed offset). However it obfuscates their relationship to each other. The only alphabetically adjacent keys found in QWERTY rows are:
- FG (102/103)
- JK (106/107)
- NM (110/109) (reversed)
- OP (111/112)
Not coincidentally, our 10 Print one-liner uses the NM pair -- because it is visible on the interface, because it is elegant and concise in the code, and because the output is surprising, given the context of maze-like computer graphics at the time. On the PET, all of the other pairs also bear related graphical characters, and we will try each of them below -- but only NM will produce something more structural than textural.
