PSI System Controls and Diagnostics
A500 User Manual
A500_UM_090115 Page 45 of 61
15
Gate Option Board
15.1 Overview
The gate option board is a full-size I/O board which connects to both expansion port connectors
of the cell controller board. It is logically connected on port 1. JPR B2 on bank 2 on the cell
controller is fitted to identify the board.
The gate board provides four independent inputs for gate (or trigger) signals on Lemo coaxial
connectors. The logic levels are TTL and the inputs have 50 ohm impedance.
The incoming gate/trigger signals are routed and used according to a software-selectable
configuration. Generally the –G option will be combined with the –R5T5 fiber optic mezzanine
card option, which provides five additional fiber optic transmitters. Each of the TTL gate inputs
can be directed to any or all of the transmitters. These fiber optic signals are then typically taken
to the gate inputs of triggerable devices connected to the A500 communication loops. If the
devices are remote from the A500, and if they all require the same trigger, then it can be
convenient for cabling to take only a single trigger line from the A500 and use a trigger fanout
unit such as the X14, local to the devices.
In addition to driving fiber optic transmitters, any of the TTL inputs can be selected to be a
trigger for the counters in the gate-counter board (see next section 16). There are no constraints
on the permutations of input to fiber optic output and counter trigger mapping.
The latency for a signal to be passed from a TTL input to a fiber optic output is about 50 nsec.
The latency from the TTL input to the response of a fiber optic receiver in a remote device is
about 200 nsec, as a result of the rise times of the fiber optic transmitter and receivers. The
further time for the remote device to capture the required data will depend upon the details of its
particular measurement process, of course.
15.2 Operation of the Gate Function Using the PTC Diagnostic
The PSI Diagnostic host program allows you to try out the gate input features. Figure 23 shows
the setup tab where the gate/trigger distribution logic can be set up. In the example shown,
trigger signals arriving at the gate input 1 (also labeled A) are used to drive the first fiber optic
transmitter only; and gate input 2/B is used to drive transmitters 2, 4 and 5 in parallel. Figure 24
shows the second situation graphically. You can in fact test the setup if you provide a DC level
at a particular input, as the selected output transmitters will illuminate in the visible (red light).
The Trigger LEDs on the setup screen also illuminate when a signal is seen on the corresponding
input.
