17 Jul
2014
17 Jul
'14
10:53 p.m.
On 07/17/2014 10:01 PM, Mark J. Blair wrote:
Do paper tape BASIC interpreters pay any attention to
the DELs when
they're loading a program, or are they just there so that the tape
can be printed legibly on teletype-style console?
Can other nonprinting characters be used in place of the DEL, like a
NUL or a 0x80 (NUL after the MSB is stripped off)? I notice that the
DELs weaken those 38-year-old tapes quite a bit.
DEL/Rubout had a well-accepted meaning in old-school ASCII/USASCII
code--and that was "delete" or "idle". If you were punching tape,
and
made a mistake, the routine was to backspace over the erroneous
characters and overpunch them with DEL/Rubout characters (all holes
punched) and then continue with the correct characters.
Ask any retired TWX or Telex operator.
In fact, ECMA-35 (1994) calls out the matter quite explicitly:
6.2.1
Fixed coded characters
Character DELETE
Name: DELETE
Acronym: DEL Coded representation: 07/15
DEL was originally used to erase or obliterate an erroneous or unwanted
character in punched tape. DEL may be used for media-fill or time-fill.
DEL characters may be inserted into, or removed from, a CC-data-element
without affecting its information content, but such action may affect
the information layout and/or the control of equipment.
So there you go--DELs are to be ignored. Whether or not everyone does
is, of course, a different matter.
--Chuck