Re: switching off the ALPHA console

On 2011-04-20 08:16, DaveG wrote:
Don't believe we've ever had a problem with Alphas and consoles either
being there or not. Like Paul, we had crash carts, then terminal
servers.

VAXen are another story but the original note mentions Apha only.

Just to make one thing clear. The halt on break behavior on a VAX is configurable. There is no reason for it to be set this way if you routinely do things like power off and on your terminal.

And to make one technical aspect clear. A serial line is normally always at -12V (nominally), which is "space" in RS-232 speak. When a characters is sent, the signal line starts with a "mark", which is +12V (nominally), which is the start bit. After that comes the data bits (how many is up to you), followed by possibly a parity bit, and then a stop bit. The stop bit is also a "space". The line is then idle until the next start bit is seen. The stop bit guarantees that you have some appropriate idle time between the last actual data bit (or parity) and the next start bit.
A break is then a "mark" that continues for longer than the data bits and parity can go on, so that you still have a mark when the stop but should be. This cause a data overrun state (you get data when the line should be idle).

Now, as you might have noted above, space is -12V while mark is +12V (still nominally). When you power a terminal off, the line will actually go to 0V. So, what does that mean? Most receivers decide to interpret that as a mark. So power off will be interpreted as a break.
But in truth, 0V should probably be interpreted as "unknown", and should not go one way or another. But we don't have three values for a binary signal.
Some terminals might also, on power up, keep the signal in the mark state until things have been initialized, which would be a proper break, although perhaps unintentional by the owner.

Johnny

--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt@xxxxxxxxxx || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
.

Relevant Pages

  • Re: switching off the ALPHA console
    ... Most receivers decide to interpret ... that as a mark. ... So power off will be interpreted as a break. ... Terminals that appear to be in a constant break upon power down on the other hand is something I have seen. ...
    (comp.os.vms)
  • Re: Why was VAX abandonned ?
    ... >> Some terminals send a BREAK when they are turned off. ... and seems to have some implementations where "current" is a MARK ... during power down or during power up, is broken, whether by ...
    (comp.os.vms)
  • Re: [40K] 1500 pt. army critique required
    ... Chaos Sorceror Lord (Mark of Tzeentch, Terminator Armor, Bolt of Change, ... Power Weapon, Three Thrall Wizards): ... Chaos Space Marines (Mark of Tzeench, Bolter), 1 Aspiring Champion ... weapon upgrades - that's what psychic powers are for. ...
    (rec.games.miniatures.warhammer)
  • Re: comparative efficiency test
    ... :>: I will if you remember to mark text you quote. ... measuring the damned power drawn from the supply ... (Torque in Nm and angular velocity in rad/s) ...
    (sci.physics)