Modern external storage emulating RX02 (was Re: Most used toys, was Re: The late, great TRS-80)
ethan.dicks at gmail.com
Wed Jun 27 15:02:14 CDT 2007
On 6/27/07, Allison <ajp166 at bellatlantic.net> wrote:
> Using a Tu58 on an -8 is not a goot match and there are lots of gyrations.
> >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.
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.
> 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.
> 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.
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.
More information about the cctalk