[SunRescue] Re(2): [SunRescue] 3/160 and Terminals

[Tim Hauber]

rescue at sunhelp.org,Internet writes:
>I run several of the old VME suns (3/110, 4/110, 3/160, 3/200), and use
>the following order:
>
>  poweron ---- terminals and peripheral drive cases and printers first
>               then the cpu chassis.
>
>  poweroff --- peripheral drive cases first, the terminals and printers,
>               then the cpu chassis.
>
>I don't use a real VT100 terminal, and memory vaguely tells me that
>on some systems (don't know the exact types right off), the VT100 power
>can blow chips.  I always use only 3 wire (T/R/G) hookups, so that may
>not be a problem, if no other signal lines are present.  My terminals
>are all WYSE, PC/kermit, or Heathkit/Zenith things.
>
>The old full-page sun docs suggest a slightly different order, but
>that always seemed to electronically make no sense to me.  On poweron my
>memory suggests that they recommend cpu on first, and peripherals second.
>I have always done it the other way around because I want to make sure
>the CPU sees the correct signals on poweron so the hardware and software
>does not get into conflict over signals being presented to the cpu during
>the transitions in peripheral signal lines on powerup.  Along the same
>thinking, I always make sure peripherial drives are spinning at speed
>and cycled to the line (from the boot posts), before turning on the
>CPU.
>
>That is all I know.  Maybe others can fill us in on any other details.
>I am sure there are historic or engineering reasons for how it should
>be done, and that can only be good information to share.
>
>Bob Keys

Electronically, there are transistor configurations that should see power
before they see signal, but in a general sense (no knowledge specific to
the machines being discussed) a serial link (or any data link on copper
wires) has virtually the same interface requirements at each end, in the
case of a terminal, you have the standard com lines, and on each line you
have an output and an input. A properly designed output will tolerate
anything from no load (open) to dead short, without damage, and will
tolerate it whether powered or not.  A properly designed input will
toleratet anything from floating to either the positive or negative
maximum they are designed to accept, and usually are designed to handle
many times that without letting out the magic smoke.  So, assuming proper
design it doesn't matter electronically.  

I have always had better luck with external devices being up first, for
the resons Bob mentioned, but some of the scsi drives I have worked with
actaully have the capability to delay their own powerup, I have seen as
much as 20 seconds.  Low power consumtion peripherals like printers and
external removable drives I tend to just leave on all the time.  

TIm hauber

"Proximity to wonder has blunted our perception and appreciation of it"
--Tim Hartnell in 'Exploring ARTIFICIAL INTELLIGENCE on your Commodore 64'