I actually have one of Bob Anderson's excellent SBC6120 boards. Getting OS/8 up and running was no problem at all. However the way the PDP-8 handles IOTs almost requires some GALs to interface it with the bus (the GALs take the PDP-8 IOTs and generate the actual addresses of the devices on the bus). You can communicate with 8-bit data IO devices by leaving off 4 bits of the 12-bit PDP8 word.
There is a *lot* of PDP-8 assembly programming that goes into making a working system where the use of "modern" peripherals is "transparent" to OS/8 so that vintage software will run properly. Bob wrote all this for the SBC6120, with the BTS6120 monitor. The HD6120 supports two types of RAM - 32 Kwords of main memory, and 32 Kwords of "panel" memory (which was intended to be used for programs that simulate the front panel operation in embedded sysyetems). The "panel memory" is mapped to a ROM on the SBC6120 which has the monitor code and the handler routines for all the "modern" hardware.
So if we wanted to put a board on the S-100 bus, I would see two options. (All of Bob's schematics and the BTS6120 software & source coe are GPL licensed):
-Recreate the SBC6120 on 1 S-100 board with the RAM, ROM, parallel/IDE and serial interface chips built in so that we could use the BTS6120 monitor unmodified, and make using our other S-100 boards a "secondary" feature that we could add at our leisure. (I think this would be relatively easy, but it kind of "goes against" the way the S100Computers.com CPU boards are done)
-Build a board with just the HD6120 and EEPROMS and use 16-bit RAM transfers and 8-bit I/O transfers to access our regular RAM, Parallel I/O, Serial I/O, CF Card, etc boards. Use BTS6120 as an example but modify the sections of code called to interface with the S-100 hardware. (I think this would be harder, one of us would have to get pretty deep into the PDP-8 assembly to make it work).
There were, I believe, 3 different versions of the PDP-11 in ICs, one with multiple ICs for the CPU and 2 with single-package solutions. The big difference is since the HD6120 was a product offered to everyone, there is a complete datasheet for it. The PDP-11 ICs were special made for DEC so while there are DEC "specification" documents, you'd need BOTH details on the CPU chip and the PDP-11 design details to build a board that would run vintage software like old Unix "out of the box".
Andrew
I recently got a quote from UTSource for HD6120s - Qty 12 = $12.50 each
On Wednesday, July 30, 2014 9:50:42 AM UTC-7, David Fry wrote:
Hi John,
both Vince and Andrew have made mention of an interest in seeing a version of DEC mini computer technology brought onto the S100 bus (if this is possible).
This idea is beginning to grow on me and I would like to add my interest to the number (now 3 :-) )
I have no experience whatsoever in this area of vintage computing, but what a trip down the history of computing it could be.
I noticed that the HD1-6120 seems to be available in small numbers (including from UT source)
and also the DCJ11 although price is somewhat higher
or maybe some other significant vintage mini...., again I'm not sure how practical a suggestion this is but with the Z80 done and the Intel x86 track done my processor interests are now covered.
regards
David Fry
On Tuesday, July 29, 2014 6:58:58 PM UTC+1, monahanz wrote:
I have been doing some long term planning as to the direction I would take in doing new S100 boards. To recap, we now have a 6502, Z80, 8080 (Josh), 68000, 8088, 8086, 80286 and soon an 80386 set of boards on the S1000 bus. Andrew and I have already started laying out an 80486 board.
Since I do a lot of flying on business I have time to read up on chips and recently I have been thinking what would be the best way to get ARM CPU's on the bus. There are many types, and while one could start with a bare chip it does seem to make more sense to start with an embedded module. There are many of these, most of which boot up Linux immediately. One particular one I'm fairly impressed with is an Italian one called "Aria G25" see:-
http://www.acmesystems.it/aria
Also it lends itself to easy pin splicing/layout on a board. It has good documentation and software support. I particularly like the fact that it has 60 GPIO pins. These could be easily spliced into our S100 bus so we could use our current boards for I/O. (In fact at 400MHz, one could also use the S100 RAM!). I know some of you will view this as sticking a Lamborghini engine in a Volkswagen, but would it not be neat to see Linus running on the S100 bus.
Comments please, in particular I would be interested in any other similar modules.
John