[Simh] Additional Interfaces for the VAX780 simulator

[Jason Stevens]

wouldn't it be easier to just talk to some kind of charicture device
via the magic of unix, and say use USB->RS232 devices to have it
automagically work?

some ancient versions of SIMH did have charicture port support.. I
remember as I ran SLIP from a cisco router to an emulated 2.11 BSD on
the PDP-11... I want to say this is when SIMH was only PDP-11...
1996? 1997? 1998?




On Tue, Apr 14, 2009 at 8:14 PM, Ethan Dicks <ethan.dicks at gmail.com> wrote:
> On Tue, Apr 14, 2009 at 5:38 PM, Gregg Levine <gregg.drwho8 at gmail.com> wrote:
>> On Tue, Apr 14, 2009 at 9:36 AM, Ethan Dicks <ethan.dicks at gmail.com> wrote:
>>> On 4/14/09, Hölscher <hoelscher-kirchbrak at freenet.de> wrote:
>>>> I would like to have two (or more) additional interfaces for the VAX780 simulator:
>>>>
>>>>  DMC-11 (for DDCMP - DECnet, would be useful for the PDP-11 as well)
>>>
>>>>  Anyone else interested in those devices, or am I the only one?
>>
>> Hello!
>> Well actually I am, Ethan. Especially the DDCMP connection.
>
> That question was asked by Hölscher, not me.
>
>> I am still curious if the connections posing as a serial one can be
>> connected to a physical device. I believe the Altair/Imsai one can be
>> connected to one such device, but I've also never had a reason to try
>> it.
>
> What I said in response is still correct - "standard" PC hardware has
> no way to speak sync serial - there are no start and stop bits, among
> other things.  The closest I suppose you could is to attempt to
> bit-bang out serial frames via a parallel port, but then you'd still
> need a level shifter from TTL to EIA levels.
>
> A UART is not USART, though some chips, like the Z8530, can be used in
> either mode.  The 8250 (and its descendants the 16450, the 16550, and
> more recent implementations that are a corner of a motherboard
> chipset) just can't emit the right bitstream to connect up to a
> classic sync serial device.
>
> <http://www.freebsd.org/doc/en/articles/serial-uart/index.html>
>
> One could whip up a virtual USART that communicated over a network
> socket or some other IPC mechanism to another instance of simh, but
> not to a real machine via a real connection, not without adding
> hardware to the machine that was running simh.
>
> If you are willing to run simh on a PC that's old enough to still have
> ISA slots, it's possible to find (or semi-easily build) a serial board
> that could do the job, given the right drivers and new code in simh.
> It's not as simple as just writing new device emulation code in simh.
> One could build a sync-serial interface on a PCI card, but that's
> nowhere near as easy as building an ISA card.
>
> -ethan
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