On Thu, 7 Oct 2004, Bob Shannon wrote: Not specifically, but related: If the generator turns off write current (eg. Z axis off) when "at rest" you can let the beam rest whereever you want. If it's a 4-quadrant system eg. location (0, 0) is X=0V, Y=0V, you can simply multiply X and Y by 0 when Z=0, aka turn off X and Y. If you're simultaneously translating from 4-quadrant to 1-quadrant (eg. (0, 0) is X=0V, Y=0V) then you can force X=Y= (fullscale / 2) whenever Z is off. Both schemes could be done with an opamp each dimension, probably re-use one already present.

On Thu, 7 Oct 2004, Brad Parker wrote: It wasn't a concern for the phosphor, but the suggestion that maybe "Z" could be used to detect when the beam is "parked" as opposed to being arbitrarily placed at (0, 0). What I meant was, if you find "Z" off (eg. nothing to be displayed) then you can put the beam in the center of the screen and save the transistors, within your adapter. In 1982, when I got a super-early IBM PC (working for Phoenix Software) the first thing I did was to burn out the fuse in the monitor with the wrong display-type DIPswitch setting... apparently the wrong horizontal freq makes the monitor draw a lot of current, by some miracle the Q didn't protect the fuse.

<snip> There is a problem with simply using the Z axis to switch the inputs to the deflection amps and center the beam. If drawing a vector starts far from the 0,0 origin, the X and Y deflection signals will be ramping up to position the beam prior to the Z axis signal unblanking the beam. So in this case the deflection amps would be presented with a very fast 'jump' while the Z axis signal had unblanked the beam. This is not a good thing. I looked at beefing up the deflection amps to allow keeping the beam at 0,0, but this is totally impractical. The power supply for the monitor is not able to supply enough power, and the deflection yolk would burn up quickly. This is a very bad thing. Fortunetly I think I have a workable plan: The HP 1350 has two signals on the AUX connector that may save my bacon. The first is an active low signal telling external equipment that the vector generator is busy. I plan on monitoring this signal to detect the end of a display update cycle. Once a display update cycle is completes, I'll activate some analog switches that will ground the X and Y axis inputs to the vector monitor, and also assert a signal that holds off vector generation until a timer expires. At that time I'll switch the HP 1350 analog vector data back to the monitor, then drop the vector generation hold signal and wait for end of display update once again. So a small microcontroller will control the refresh rate, and give the monitor plenty of time for the deflection amps to cool down between display refresh cycles. I had already thought of a simple state machine that would do something similar to the Z axis signal in case deflection power to the monitor was lost while a Z axis signal was still present. This will cause major screen burn on this type of monitor because the high voltage supply remains high for some time after power-off, but the spot-killer circuit drops out as soon as deflection power is lost. In my application the monitor is not in the same rack as the HP 1350, so a power sequence problem is quite possible. So now I think I'll move all these functiuons into a small microcontroller, and kill both problems with one solution. The only down side to this is that this approach will only work with the HP 1350, my Imlac PDS-1 does not have these external handshake signals. But thats ok, I have a new-old-stock Tektronics 611 storage tube I can use for the Imlac. Imlacs could be ordered from the factory with Tek 611's in place of the stock vector display, and its a 'period' device, unlike the WG 19V2000.