Document type:
Title:
Revision date:
Revision:
User's Manual (MUT)
Mod. V812 16 Channel Constant Fraction Discriminator
20/04/2009
4
NPO:
Filename:
Number of pages:
Page:
00101/97:V812x.MUTx/04 V812_REV4.DOC
23
20
4.5. Test, Veto and Or signals
Some operations can be performed by sending two external NIM signals:
•
TEST
: an input signal sent through this connector triggers all the enabled channels at
once. This feature allows to test of the module as well as to generate a pattern of
pulses suitable to test any following electronics.
•
VETO
: an input signal sent through this connector allows to veto all channels
simultaneously. A veto pulse of width T will inhibit the input channels for a period with a
T duration. Its leading edge must precede the input signal leading
edge by at least 8 ns and overlap completely the input signal.
•
An
OR
output connector provides also the logical OR of the output channels. The
relevant "OR" LED lights up if at least one of the enabled channels is over threshold.
4.6. Channels
test
It is possible to obtain pulses on all channels:
•
by sending a NIM pulse through one of the two “TEST” connectors located on the front
panel.
•
by performing a Write operation at (Base a %4C).
4.7. Setting the threshold
For each channel of the V812 the discriminator threshold is set up via an 8 bit DAC. The
threshold values can be programmed in a range from -1 mV to -255 mV with -1 mV steps (set
values: 1 to 255). As in all Constant Fraction Discriminators, these thresholds are to be set
above the noise level: they do NOT correspond to the actual level that triggers the discriminator
outputs, the latter being a “constant fraction” of the input signals.
In order to write the Threshold for each channel, the User must perform a VME access at
(Base a %00 to %1E).
4.8. Setting the output pulse width
The output pulse width is adjustable on 8 bit from 15 to 250 ns (set values: 0 to 255) and the
chosen value is applied to each group of 8 channels each. It can be set at Base a %40
for channels 0 to 7 and at Base a %42 for channels 8 to 15. The set value corresponds
to the Width as follows: 255 leads to a 250 ns value, 0 leads to a 15 ns value, with a non-linear
interpolation for intermediate values.
Note:
TEST and VETO are high impedance inputs and each one is provided
with two bridged connectors for daisy chaining; the chain has to be terminated
on 50 Ohm on the last module; the same is needed also if one module only is
used, whose inputs have thus to be properly matched
