Re: PDP-1 Spacewar

[George Robbins <grr@shandakor.tharsis.com>]

> Date: Mon, 04 May 1998 13:13:16 -0400
> To: deltoids@mcws.net
> From: Aron Insinga <ainsinga@infomation.com>
> Subject: Re: PDP-1 Spacewar
> 
> At 11:36 AM 5/4/98 -0400, you wrote:
> Remember the early home-built null modems that we had at Project Delta?
> Aluminum boxes with a toggle switch for Carrier Detect and a pushbutton for
> Ring Indicator, I think.  (I guess that DEC sold them but they were
> expensive.)

Heh...  That was on of my projects.  For reasons not really clear,
RSTS took the "active" approach to making the modems answer - instead
of just leaving DTR high and waiting for a call to come in, they left
it low and waited for the RI to signal a "ringing" condition, then
raised DTR to permit the modem to answer.

So anyway, the button was needed to simulate a "call" when you wanted
to log in locally.  DEC null-modems didn't have buttons, they were
just big & expensive cross-over boxes. "Local Terminals" weren't supposed
to need this because they were "current loop" interfaces, but we got
CRT's that had RS232 interfaces.

Associated with this was another story about RSTS perversities.  When
the CRT's first came out, they were't particularly fast - the Datapoint
was 2400 baud, if I remember, but I think the VT05 could do 4800 or
9600 (with padding).  On of the guys from DEC spent quite some time
explaing to us how *bad* the idea of running termninals at 9600 baud
was - they'd be jerky since the computer couldn't be expected to do
continuous 9600 baud output, and also who it would bog down the system
doing I/O that fast.

He's probably using a k56flex modem at home now. 8-)

						George