19 Nov
2005
19 Nov
'05
3:20 p.m.
Subject: Re: Which paper tape hole is bit 1?
From: "Barry Watzman" <Watzman at neo.rr.com>
Date: Sat, 19 Nov 2005 09:50:58 -0500
To: <cctech at classiccmp.org>
I have a chart of paper tape hole patterns for all 128 characters, and it
shows the LSB (bit zero, although the chart numbers them 1-8) as the edge
hole on the 3-hole side, with the bits in order 0 to 7 (or 1 to 8).
However, one question, this chart shows the high-order bit (parity bit)
punched for every character, no exceptions. Was that a standard convention
in sending ascii files to paper tape?
There were three, even, odd and stick (usually 1 but could be 0).
TTY when used with PDP-8 was stick at 1 (hole).
PDP-8 convention was stick at 1 (hole) for ascii
PDP-8 RIM format channel 8 is not used and channel 7 signals addres
or data pair (lower six bits x4 for 12 bits address and 12bits data).
This allows the 4 six bit pairs to specify and address and data
anywhere and non consecutively.
PDP-8 BIN format bit 7 was 2 6bit addresses to follow and then the
rest are data (six bit pairs). The address is an origin and the
data follows in sequential locations.
Nominal PDP-8 use was short BIN loader hand toggled in. Load bin
tape that contains small BIN format program or loads the RIM
loader for more complex programs (basic, focal). BASIC would
then read an ascii program tape.
Some systems the 8th hole was used for data.
PDP8 convention for hole numbering is outside 3 hole side is 1 and
numbered through 8 across.
1 2 3 S 4 5 6 7 8
Allison
19 Nov
19 Nov
5:06 p.m.
From: "Allison":
Nominal PDP-8 use was short BIN loader hand toggled
in. Load bin
tape that contains small BIN format program or loads the RIM
loader for more complex programs (basic, focal). BASIC would
then read an ascii program tape.
It's a nit, but you have the roles of BIN and RIM reversed in
this paragraph. You also omitted a discussion of the checksum,
field setting, and comment features allowed in a BIN tape :-).
For those who care, BIN tapes have an extra 'data' pair at the
end which forms a checksum. Bytes with both of the most significant
bits set use the next three bits to select which bank or 'field'
is loaded. And arbitrary 'comments' may appear between rub-outs
(which have all bits set). RIM tapes have none of these features.
Both BIN and RIM tapes use leader-trailer with just the MSB set.
There are at least two versions of the BIN loader. I don't know
offhand if the older BIN loader supported all the features or
not.
Vince
5:35 p.m.
vrs wrote:
From: "Allison":
I flubed the first one and 99% get it wrong when playing with the -8!
The other was one of those typing things where I decided it was enough
and stopped rather than get even further off the topic.
Allison
Nominal PDP-8 use was short BIN loader hand
toggled in. Load bin
tape that contains small BIN format program or loads the RIM
loader for more complex programs (basic, focal). BASIC would
then read an ascii program tape.
It's a nit, but you have the roles of BIN and RIM reversed in
this paragraph. You also omitted a discussion of the checksum,
field setting, and comment features allowed in a BIN tape :-).
For those who care, BIN tapes have an extra 'data' pair at the
end which forms a checksum. Bytes with both of the most significant
bits set use the next three bits to select which bank or 'field'
is loaded. And arbitrary 'comments' may appear between rub-outs
(which have all bits set). RIM tapes have none of these features.
Both BIN and RIM tapes use leader-trailer with just the MSB set.
There are at least two versions of the BIN loader. I don't know
offhand if the older BIN loader supported all the features or
not.
Vince
6986
days inactive
6986
days old
2 comments
2 participants
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vrs＠msn.com