Philips PM3320 Operating Manual page 121

4-101E
Direct mode dual channel
In dual channel mode, register RO consists of 2x 2048 locations. (2048 locations per channel).
Now, 2048 samples are taken simultaneously on each channel and placed in register RO.
The first 2000 samples of each channe! are displayed over 10 divisions on the screen.
In the time base range 500 us/div .. 200 ns/div a sweep consists of 2 x 512 samples.
Now the samples are placed on register locations 0, 4, 8, 12 and so on. The other locations are
filled with interpolated "samples" and not displayed if DOTS is on.
In the time base range 500 us/div. ... 200 ns/div. the interpolated samples can be replaced by real
samples if the input signal has a repetitive character. This is called MAXIMUM RESOLUTION.
If MAXIMUM RESOLUTION is selected, the pilot lamp REP ONLY is on.
In single channel mods the first sample of a sweep can be piaced on location zero, as well as on
location seven. To determine on which location the first sample should be placed, the time which
elapses between the trigger pulse and the first sample pulse is measured by the internal delta-t
circuit. A very short time results in placing the first sample on the first location, a longer time
results in placing the first sample in a higher location. (see fig 4.47).
During the next sweep, again 512 samples are taken and placed in the register. Ifthe samples are
placed on locations where already has been placed a sweep of samples, the old samples are
overwritten,
If AVERAGE is selected, the old sample and the new sample are used to calculate a new sample
(see also section 4.3.12).
So it takes at least 8 sweeps, but probably more, to make a complete picture.
i
|
I
|
|
(
|
_-t + + + + + a
"7 1 ~
- s
c 1 se
} ee
: } :
1 | i
' I |
Ly
+7157 sweer
|
+- 2NO sweep |
Dc a ees
el-[s|s|+/«(=/=/sletsle(s/eie[ele(slelefa(s[Rial = a]
Bia a a
wg a w
ale « Ed
416 5 a
818 8 8
=|2 z 2
z
Figure 4.47 Maximum resolution mode after two sweeps.