27 Jun
2025
27 Jun
'25
10:37 p.m.
On Fri, Jun 27, 2025 at 8:39 PM Adrian Godwin via cctalk
<cctalk(a)classiccmp.org> wrote:
Interesting that some readers didn't require the sprocket hole. Whilst
I have never seen a paper tape reader that didn't use the sprocket
hole as some kind of reference. Either by driving the tape using it or
by detecting it along with the data holes.
I can appreciate that they didn't mechanically
drive on it, I assumed
they'd use it as a clock signal to sample the data levels. Even that
could be avoided, but then a nul would be indistinguishable from the
space between punch positions.
Did they make nul an illegal character, or determine it using a
flywheel sync ? I appreciate there were out-of-band ASCII characters
such as EOT but weren't there binary format tapes too ?
Card readers (a totally blank column is legal on a normal 80 column
card) took a reference from the leading edge of the card and re-synced
whenever holes were found (see the Documation manuals on bitsavers,
for example). But paper tape? You could re-sync on the data holes and
hope for the best but why on earth would anyone bother when every
paper tape has the sprocket holes?
If a paper tape reader that doesn't need sprocket holes exists, could
somebody post the make/model and preferably a link to a manual for it.
-tony