27 Jun
2007
27 Jun
'07
3:42 p.m.
Subject: Modern external storage emulating RX02 (was Re: Most used toys,was Re: The late,
great TRS-80)
From: "Ethan Dicks" <ethan.dicks at gmail.com>
Date: Wed, 27 Jun 2007 11:14:19 -0400
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
On 6/26/07, Dave McGuire <mcguire at neurotica.com> wrote:
I was just reading some old list threads about PDP-8s and TU58s and
emulators - transfer speed aside, the real problem was that most
pre-OMNIBUS PDP-8s didn't have a spare serial port (just the console
TTY), and that the serial hardware needs to be able to send a Break to
the TU-58 to properly initialize and reset the controller in the
TU-58, and unmodified PDP-8 hardware can't do that. I did run across
a bunch of old 12-bit SIG newsletters from when the TU-58 was new, and
all the gyrations folks went through to be able to use them, since at
the time, they were about the cheapest mass storage you could get from
DEC. One entire aspect of the project was how to mod M706/M707 or
KL8E serial interfaces to generate a break. Another aspect was trying
to wedge a driver into a couple of pages of code.
Using a Tu58 on an -8 is not a goot match and there are lots of gyrations.
Serially
connecting would rot though...
Yeah, kinda.
If all PDP-8s had a spare serial port, it might make sense to have a
serially-attached modern mass storage peripheral.
Adding a second serial is trivial as there were many differnt serial
cards available. To make a TTY card RS232/432 passable is also not hard.
Since that's
nowhere near universal, it frequently comes down to deciding on which
models to support. One of the few disadvantages of the PDP-8 spanning
1965 to 1994 (PDP-8 to DECmate III) is that there's a huge variety of
hardware that all runs the same instruction set (give or take a couple
instructions), but with an equally huge variety of default peripherals
and expansion options. An RX01/RX02-attached device, at least, will
work with OMNIBUS machines as well as the VT78 and DECmate I - overall
not a bad range to cover.
-ethan
What is possible now is a small micro and a big static ram of 512k are
which fairly easy to find it's not unreasonable to simulate a RX02
using a micro at the end of a serial line (or parallel) and NOT use
the protocal of TU58. The cpu/micro used does not have to be very high
powered or fast as all it's doing is data transfer and PDP-8 PIO is
usually slower than 30-40K words/sec.
In the end what is used is more a matter of convenince than technology.
I happen to be lucky(?) as my 8f has two serial cards but nothing
else device wise. One of th cards is the usual console TTY but the
other is a UART based M8652 that were often used for modem
banks and serial data concentrators/switches made using PDP-8s.
Allison