Products > Test Equipment

Tektronix 2465 MAME emulation

<< < (7/7)

siggi:
While you have the subject on the slab, I'm wondering what is the condition that fires an auto sweep. From looking at the signals between the display sequencer, the trigger hybrid and the sweep hybrids, I'm thinking that it has to be THO transitioning low. This would mean the display sequencer has direct control over the frequency of auto sweep, which almost certainly is related to the reciprocal of sweep speed to maintain something like a steady auto trace brightness across sweep speeds.

Seeing how THO goes to both the trigger and the A-sweep hybrid, my bet is that THO transitioning low to the sweep hybrid is what triggers the auto sweep. Looking at the sweep hybrid schematics, it looks plausible that a low THO would initiate a sweep?
I guess to validate this, you'd need to look at THO in auto sweep vs the trigger hybrid output?

siggi:

--- Quote from: MarkL on March 09, 2023, 10:36:12 pm ---The x11x pattern is latched for one poll cycle, then on the next poll it shows the "now" pin state again.  The x11x state I think is to let the processor know a transition happened  between polls on /SGA. /TSA, or /TSB.

--- End quote ---

Ah, I get it now. Either state of each line (except B sweep) is represented as a latched bit in the trigger status reg. So a set bit means that a particular state occurred and was latched for a particular signal. So a x11x pair means both states occurred from last read.

I was wondering why the B-sweep doesn't get the same treatment, but then I realized it shouldn't need to, as the B sweep should always be bracketed by the A sweep.

MarkL:

--- Quote from: siggi on March 10, 2023, 02:40:29 am ---...
Seeing how THO goes to both the trigger and the A-sweep hybrid, my bet is that THO transitioning low to the sweep hybrid is what triggers the auto sweep. Looking at the sweep hybrid schematics, it looks plausible that a low THO would initiate a sweep?
I guess to validate this, you'd need to look at THO in auto sweep vs the trigger hybrid output?

--- End quote ---
I'm seeing that the U500 trigger hybrid output, /TGA (pin 18), is static low when the scope is auto sweeping.

/SGA going low indicates the beginning of the sweep, and comparing that to THO it's difficult to say who's first due to the vastly different edge speeds of 18ns vs. 74ns (see below).

THO does start to drop first, so it's conceivable the sweep hybrid is switching on an unusually high (non-TTL) voltage threshold.

EDIT: Let me clarify and say that THO falling is obviously not a result of /SGA falling, but it is not a foregone conclusion that THO falling is causing /SGA to fall.  Only that the timing does support the latter as a possibility.

siggi:

--- Quote from: MarkL on March 10, 2023, 11:59:54 pm ---/SGA going low indicates the beginning of the sweep, and comparing that to THO it's difficult to say who's first due to the vastly different edge speeds of 18ns vs. 74ns (see below).

THO does start to drop first, so it's conceivable the sweep hybrid is switching on an unusually high (non-TTL) voltage threshold.

--- End quote ---
Yeah, I guess the falling edge of THO is not very time critical, but presumably the rising edge has to be crisp for the trigger and sweep hybrids to be sequenced correctly for a sweep.

I think this confirms that the display sequencer initiates auto sweep through THO, at least the data doesn't contradict that hypothesis :).

Now, looking at the tek_made catalog info sheet again, I found this:

Ramp Initiation Sweep Gate Circuitry
Ramp is Initiated by the coincidence of a “LO” at the “Not Trigger”, “Not Auxiliary Trigger" and “Trigger Holdoff” inputs.

which seems to further confirm that the falling edge of THO will initiate a sweep if the trigger strobe didn't beat it to it.

siggi:

--- Quote from: siggi on February 26, 2023, 04:40:10 pm ---The other feature is "TRIGGER SLOPE SELECTION", where it seems it would be possible to select different trigger slopes for each delay sweep. I don't think the scope offers the possibility of selecting trigger slope per delay sweep - though I may be wrong about that.

--- End quote ---
So it turns out that in the presence of the CTT option, the 2465 does offer the possibility of triggering on alternate slopes for dual B delay sweeps.
Likewise, in the presence of the CTT option, my 2467 allows setting distinct slopes AND trigger levels for each of the delay sweeps. This allows e.g. automated measurement of pulse width, or - possibly - say automated rise time measurement. The latter would be fairly touchy, though my 2467 does display the trigger level voltage as I'm adjusting it.

As an aside, I find myself pondering how the CTT option does delta delay measurements, for triggered B sweeps in particular. Since the delay sweeps alternate, there's no way to directly measure the time from one B trigger to the other that I can think of. I guess the CTT option has to measure the A to B trigger delay for each delay/trigger/slope setting and then compute the difference?

Navigation

[0] Message Index

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod