27 Jun
2007
27 Jun
'07
3:47 p.m.
Subject: Re: 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 16:02:14 -0400
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
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.
If you have a parallel port or even an interface to read/write one bit
with an IOT (less parts than parallelport or tty interface) there are
possible interfaces even for 8s.
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. 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.
20ma works too. Though it's not hard to pick up the TTL or logic
before 20ma conversion.
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
DCKAA, have to look that one up.
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.
If the driver were developed for the device it could be anything.
For example the device could be two parallel output and one input
port. One output port sets the block address (128word block for
512kW) and the second is read/write to ram data with auto increment
to the low block counter. That would be PIO, no micro and two
512k byte wide rams (4bits wasted) and 5 74LS161s as the ram
address counter (modulus 128). There are existing pdp8 parallel
IO cards that can do that.
When it cools down and I get a few minutes that might be an easy
board to try and build. I imagine patching OS/8 is not hard as
the device page is locatable. Though the complete package would
need a test program, formatter and a device driver for OS/8.
Allison
-ethan