My source pertaining to the serial bus on the S being the basis for the Omnibus I got straight from the FAQ. To be more specific it pertained to the easy configurability of the 2 busses.
On Sep 8, 2016 10:27 PM, "Johnny Billquist" <[email protected]> wrote: Bob, you are right in that the PDP-5 used address 0 for the PC, and put the saved PC at address 1 at interrupts, which is not compatible with the PDP-8, and means any interrupt driven code will not work across the PDP-5 and PDP-8. Not sure what you mean by 0/1 for interrupts. Maybe you mean that 0 is where the pre-interrupt PC is saved, and execution starts at 1? Anyway... As far as the early PDP-8 models go, the 8/S is the odd ball out. As far as I can remember, a bunch of OPR combinations did not work the same (or at all) on the 8/S, compared to any other PDP-8 model. So special care needs to be taken when you write something for an 8/S. Apart from that, the machines are mostly upward compatible, indeed. The Omnibus machines added a few new things, but yes, you normally use various undocumented opcodes to tell the machines apart. RAR RTR is the one I know the best, but there are probably others too. Kermit-12 is a good source if people want to check how to tell which model it is running on, since that program does a pretty decent job of identifying pretty much all machines. Ray Jewhurst mentioned that the serial bus of the 8/S was the basis for the Omnibus - that is backwards and wrong in several ways. First of all, I'm not sure the bus was serial on the 8/S. The CPU was serial. Second, the Omnibus is most definitely not serial, and I also seriously doubt there are any relationship at all between the Omnibus and anything on the 8/S. Third, I have some vague memory that the Negibus was used on 8/S, but I should probably look that up. Johnny On 2016-09-09 03:53, Bob Supnik wrote: > The PDP-5 is, in fact, not all that compatible, because it used memory > location 0 as the PC, pushing the interrupt locations to 1/2, instead of > 0/1. So any program requiring interrupts will not work on a -5 vs an -8. > The PDP-5 had an IO halt/restart facility, modeled on the PDP-1 and > dropped from the PDP-8, which allowed an IOT to "wait" for completion > without looping and testing a flag. It does not seem to have supported > an EAE or extended memory. > > The PDP-8 family (8, 8/S, 8/I and variants, 8/E and variants, 8/A) are > superset compatible for defined operations. It's possible to tell them > apart based on their behavior on undefined operations. The code for > identifying a PDP-8 is out there, but I don't have it at hand. I > remember that the behavior of RAL RAR and RTL RTR was one way of telling > the 8, 8/S, and 8/I apart. > > Most of the work for supporting models would be in the peripherals, > particularly the ones that are 'compatible' across the line (reader, > punch, terminals, clock). The pre-Omnibus machines used the older style > IOP1, IOP2, IOP4 pulse methodology; the Omnibus machines can decode all > 8 possible combinations. Beyond that, peripherals tended to be distinct: > the RK8 for the 8/I vs the RK8E for the Omnibus machines; the Type 552 > DECtape controller for the -5 and -8 vs the TC01/TC08 for the later > machines. > > The "CMOS 8s" are a whole different kettle of fish. They were only used > in word processing/DECmate systems and had many unique features. > > /Bob > > On 9/8/2016 9:10 PM, [email protected] wrote: > >> Message: 1 >> Date: Thu, 8 Sep 2016 18:57:52 -0400 >> From: Ray Jewhurst<[email protected]> >> To: simh<[email protected]> >> Subject: [Simh] PDP-8: The possibilities? >> Message-ID: >> <camfeaable-s+qszmm4axyr8pqhx3dpkiadjb_auxqo5hahe...@mail.gmail.com> >> Content-Type: text/plain; charset="utf-8" >> >> After both reading and participating in some recent discussions, I got to >> thinking that maybe the array of PDP-8 models could be better >> represented. >> I say this because from what I have read very early PDP-8 code is not >> 100% >> compatible with later models conversely the PDP-5 is compatible with the >> early code and likewise uses a negibus like the Straight-8. I thank this >> could be a rewarding experience for some of us and since I can't work I >> would be able to help coordinate, write pseudo code and beta test. If >> anyone is interested in this let the discussion begin. >> >> Thanks >> Ray >> > > _______________________________________________ > Simh mailing list > [email protected] > http://mailman.trailing-edge.com/mailman/listinfo/simh > -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: [email protected] || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol _______________________________________________ Simh mailing list [email protected] http://mailman.trailing-edge.com/mailman/listinfo/simh
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