The answer to:-
Does it need to see two characters there?
Do they have to be DEL?
Is almost certainly "NO", but I would preserve them, as removing them
destroys the historical integrity of the images....
Dave
G4UGM
-----Original Message-----
From: cctalk-bounces at
classiccmp.org [mailto:cctalk-bounces at
classiccmp.org]
On Behalf Of Philip Belben
Sent: 18 July 2014 10:28
To: General Discussion: On-Topic Posts Only
Subject: Re: Encoding of BASIC source code on punched tape
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.
Chuck, loads of interesting stuff, but it doesn't answer Mark's question.
What Mark needs to know is:
When the IMSAI (or whatever machine) reads these tapes in to run them in
BASIC,
Does it need to see two characters there?
Do they have to be DEL?
There are three possibilities that I can see:
1. No, the machine just reads the tapes and ignores DEL.
2. Yes, they can be anything, the machine ignores the first two characters
after a CRLF.
3. Yes, they have to be DEL, the machine checks this.
I think the first is the most likely, since the machine is supposed to
ignore DEL anyway, and this doesn't require any extra code. The machine
should accept the input from the tape reader just as if you were typing it
at the keyboard - if your terminal is an ASR33, the machine can't actually
tell, after all!
But you never know. It may even be different on different machines /
versions of the system.
Incidentally, when I had an ASR33 as my only printing device (bit banging
over the PET user port), I never sent any non-printing characters after
CRLF. If I'd used LFCR (as many systems do), that would have been a
different matter...
Philip.