On 8/16/17 9:38 AM, Ethan Dicks wrote:
On Tue, Aug 8, 2017 at 8:35 AM, allison via cctalk
<cctalk@classiccmp.org> wrote:
Note: TU58 (variant of DC100 tape) to my knowledge was never used with PDP-8
in any flavor. There is no reason why not other than no driver and it 8bit
only and the blocking is 512bytes.
I remember a lot of discussion in PDP-8 user group newsletters about
the TU-58 when it came out (due to cost, size, and convenience), but
one technical problem dominated the articles - how to generate a break
from various types of PDP-8 serial ports. ISTR some of the talk was
around hacking the hardware to make it possible (jamming multiple
nulls into the transmit latches without waiting for the previous one
to complete, for one).
In the end, I think it never worked out to be a favorable peripheral
to go with, perhaps because floppies got cheaper and easier and older
machines declined in active use.
-ethan
it was odd and optimized for 16/32bit machines of the day. The transfer
speed for a well buffered system was limited to about 25kbits/S average.
Without buffering or low response the rate was easily much less. On the
whole
I've limited TU-58 to physically small Qbus PDP11 systems as its
painfully slow
but very portable (even RX02 is heavy).
For modern implementation it would be easier to take an Arduino or R-PI
and match the serial limitations of the PDP-8 with a more suitable protocol
and also handle 8/12bit more transparently. That and large storage using
SD or microSD would be very cheap. Over ten years ago I went the route of
a simple serial using 8749 and a 128kx8 ram to store 6bit half words
in an block addressable form (256 6bit or 128 12bit words). It didn't
try to emulate a popular PDP-8 storage so it was easy to get going. Today
I'd use Arduino and either battery backed up ram or SD.
The alternate to that in modern hardware is to emulate the DF32 using
three cycle data break. The actual storage can be a pair of 8bit ram as a
12 bit wide memory wich is cheap and easy as cmos parts for 32K bytes
abound and larger to 1mb can be found easily. A PDP-8 with 128K words
of very fast no latency "disk" would be a interesting. The basic hardware
can be copied from the 3cycle databreak foundation module. Most of the
PDP-8 OSs supported DF32 if only for swap.
Allison
