Modern external storage emulating RX02 (was Re: Most used toys, was Re: The late, great TRS-80)
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
27 Jun
27 Jun
8:02 p.m.
New subject: Modern external storage emulating RX02 (was Re: Most used toys, was Re: The late, great TRS-80)
On 6/27/07, Allison <ajp166 at bellatlantic.net> wrote:
It's trivial from the OMNIBUS days onward to add another serial port.
Not so trivial for a Straight-8, an -8/S, an -8/L or -8/i. One may
argue that machines that old don't matter so much, but I do happen to
have a BM08 on one --8/L (total of 12K) and would like to be able to
bring up OS/8 on it someday. I'd also like to expand my -8/i to have
8K of core (and perhaps a full 32K eventually) and bring OS/8 up on
that as well.
Changing out 20mA for RS-232 isn't hard at all with the older machines
- Vince Slyngstad made some EIA paddle cards for pre-OMNIBUS boxes. I
have at least two of his cards. Some day, I'll find the time to
assemble them, but for now, I'm fine with hanging a VT220 off of my
-8/L with a 20mA cable.
Using a Tu58 on an -8 is not a goot match and there
are lots of gyrations.
Agreed.
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. 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.
Sure. There's no requirement to use the TU58 protocol, it's just
understood, is out there, and happens to work with a real device. If
you are going to write an OS/8 driver anyway, there's no reason to
stick with a protocol that's hard to use. I just dredged up an old
thread in my reading where someone suggested the TU-58 as the
"obvious" device for a diskless PDP-8. I was just heading that debate
off at the pass, since it was extensively investigated over 20 years
ago and determined to be difficult, technically.
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.
Certainly not if you are rolling your own interface. If you are
trying to make a plug-compatible RX02 emulator, there might be some
bit-level stuff that's timing critical, but the overall bandwidth is
rather low by modern standards.
In the end what is used is more a matter of convenince
than technology.
Agreed.
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.
Nice.
In amongst all the other recent PDP-8 discussions, I have to wonder
that if one was going to be spending $$$ on a 1 sq ft. PCB with edge
fingers and whatever line drivers, what would be a good choice of
peripheral options to stack on the same board. For example, the
DKC8AA has several independent devices on one hex-height card. In a
quad-height form factor, one could easily stuff two RX8Es, and at
least one, if not two KL8Es, which should take care of a lot of
external I/O requirements. The RX8Es would use the standard OS/8
driver, of course, simplifying that aspect of things, but then one
could attach that to either a real RX02 if you had one, with floppies
to read/write, or to an off-board RX02 emulator as we've been
discussing. Personally, I don't have even one RX8E per OMNIBUS
machine, so alternatives are an interesting direction for me.
-ethan
8:43 p.m.
New subject: Modern external storage emulating RX02 (was Re: Most used toys, was Re: The late, great TRS-80)
On 27 Jun 2007 at 16:02, Ethan Dicks wrote:
In amongst all the other recent PDP-8 discussions, I
have to wonder
that if one was going to be spending $$$ on a 1 sq ft. PCB with edge
fingers and whatever line drivers, what would be a good choice of
peripheral options to stack on the same board.
Why not a bunch of address decoders and latches and an MPU to allow
one to emulate whatever device one wanted?
Cheers,
Chuck
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