Racal Instruments 1260-100 Manual page 47

Signals
All communications signals are connected in parallel to the two plug-ins, except LBOARDSEL1 and
LBOARDSEL2. These two signals route to their respective plug-in slots, and identify which plug-in
is currently addressed.
The Mezzanine also provides an analog bus. This bus consists of four pairs of PCB traces that
daisy-chain from one plug-in to the next, connecting to the two slots in parallel. Each pair of traces
is impedance-matched to 100 ohms, and is routed for maximum isolation and minimum crosstalk.
Mezzanine PCB Assembly
Local Bus Signal Routing
The Mezzanine connects +5V, +12V, and +24V power from the VXIbus backplane to the plug-ins
and connects the VXIbus backplane signals to the Option-01T if it is installed.
The Mezzanine also provides the circuitry to interface between the plug-ins and the Option-01T. It
receives the local bus signals from the Option-01T on connector P2A. From J2A, the signals go to
the interface circuitry.
DIP switches S1 and S2 allow the Option-01T to be daisy-chained to the next VXI module to the
right. If all segments of DIP switches S1 and S2 are closed, the local bus signals will also go to
P2C, which connects to the VXIbus backplane. In this case, the VXI module immediately to the
right of the 1260-101 Carrier has access to the local bus signals from the Option-01T. If the
module to the right of the 1260-101 Carrier is not meant to be controlled by the Option-01T, then all
segments of DIP switches S1 and S2 should be open.
The local bus signals LBUSC00S through LBUSC09S are differential. U2 converts LBUSC00S
through LBUSC07S to TTL levels. LBUSC08S and LBUSC09S are a bidirectional differential pair.
U3 and U4 receive and drive these signals, respectively.
Reset Circuit
U7 is a voltage monitor used to reset the Mezzanine and plug-ins at power turn-on. At power turn-
on, it drives LLOGICRST low for approximately 130ms. It then takes LLOGICRST high and leaves
it high, unless +5V power drops below 4.5V.
The signal LBUSC10S is an open-collector line from the Option-01T. During power turn-on, the
Option-01T drives LBUSC10S low for about 100ms, then allows it to be pulled high. While
LBUSC10S is low, it resets all relay drivers on all plug-ins to the inactive state, opening all relays. It
also clears all outputs on digital test plug-ins to a known state.
LBUSC10S also serves another function when a plug-in asserts a global reset during an
emergency reset event. When such an event occurs, the plug-in drives LBUSC10S low. It leaves
it low until the event has passed and the Option-01T firmware clears the reset latch in the plug-in.
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1260-100/101 Adapt-a-Switch Carrier Module User Manual