9 Feb
2017
9 Feb
'17
2:37 p.m.
On Thu, Feb 9, 2017, at 07:26, Lars Brinkhoff wrote:
Michael Kjörling <michael(a)kjorling.se> writes:
And for where ^? for DEL comes from, (0377 + 0100) & 0377 == 0077 [where
the first 0377 is the control character of interest.] I am sure I've
seen code that calculates the character to be displayed in precisely
this way, but I can't remember where.
In fact, this is exactly how the control key worked on early terminals
(I recently had reason to look up an ASR-33 manual). The Shift key
toggled the 0020 bit (so shift-2 is " - if you look at the relevant
slice of an ASCII table), resulting in shift-K is [ (which did not have
a dedicated key) and shift-ctrl-K is ESC (which did have a dedicated key
as well, but the other non-letter control characters did not, and were
on shift-ctrl-LMNOP).
There was a mechanical lockout for keys that shift didn't make sense
with - all other letters and zero (which would otherwise have produced a
space), and one for ctrl (which locked out all the number and symbol
keys)
That wouldn't have anything to do with how
^@ is a somewhat common
representation of 000, would it? (Yes, using octal on purpose.) I've
always kind of wondered where that notation came from. That ^A
through ^Z were representations of 001 through 032 makes more sense.
Look at two slices of the ASCII table: