Vaisala RVP900

USER’S MANUAL__________________________________________________________________
310 _________________________________________________________________ M211322EN-D
PLL gates, etc. The writable waveform table makes the RVP900 unique, in
that the detailed timing of trigger and related control signals can be easily
adjusted in software, without having to resort to reprogramming PROMs.
This makes it possible for user software to edit the trigger timing in a
convenient interactive manner.
Trigger waveforms are loaded using the TRIGWF command. Four bits in
the command word (PW0 through PW3) select which pulse widths will
receive the new waveforms. On power-up, all four pulse widths are
initialized to user-selected waveforms.
The first word following the TRIGWF command specifies the transition
point of the POLAR0 polarization control signal. This control signal is
either held low or high for the cases of fixed horizontal or vertical
polarization, or it alternates from pulse to pulse for fast-switching
polarization measurements such as Zdr. The transition point is specified as
a value between 0 and 2047, where 1024 represents range zero. These units
are the same as the time units for the waveforms which follow, that is, a
2048-word array holding 6-bit trigger patterns. Bit 0 in each of these words
affects the TGEN0 digital output line, bit 1 affects TGEN1, etc. The bits
are output at a 7.195MHz rate, and the beginning of the 1024th array word
(1025th word following the command) corresponds exactly to the instant
at which data at range zero are sampled by the RVP900. Note that the
output rate can also be interpreted as a new bit coming every 1/48 km. In
some cases this is a more useful view.
As an example, suppose we wish to make the TGEN0 output be a 0.42
microsecond pretrigger pulse, with a rising edge exactly five microseconds
prior to range zero. This would be done by setting bit 0 in input words 988,
989, and 990 following the TRIGWF command, and leaving all other bit
0's clear. Further, if TGEN1 was to be a 0.14 microsecond marker strobe
at 20km, we would simply set bit 1 of input word 1984.
0916-149
H This bit defines the sense of the control line when
horizontal polarization is selected.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| |PW3|PW2|PW1|PW0| | 0 1 1 0 1 | Command
|_______________|___|___|___|___|___________|___________________|
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| H | | Transition Point of POLAR0 Control Line | Input 1
|___|_______________|___________________________________________|
H