[Simh] PDP-8: The possibilities?

[Ray Jewhurst]

What I was going on for the 5/8 similarities is some documents that I have
found on Bitsavers referencing paper tapes that had both an old (PDP-5) and
a new  (PDP-8) part number and I thought it would be neat to have a basic
PDP-5 simulator to help one learn the differences between the two systems.
Well off to doing more research.
Thanks
Ray

On Sep 8, 2016 9:54 PM, "Bob Supnik" <bob at supnik.org> 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, simh-request at trailing-edge.com wrote:
>
>> Message: 1
>> Date: Thu, 8 Sep 2016 18:57:52 -0400
>> From: Ray Jewhurst<raywjewhurst at gmail.com>
>> To: simh<simH at trailing-edge.com>
>> Subject: [Simh] PDP-8: The possibilities?
>> Message-ID:
>>         <CAMFEAABLe-s+qSZmm4AXyR8Pqhx3dPkiaDJb_aUXQo5hAHEt1g at 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
>>
>
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