VXI VT1433B, User Manual, Page: 95 / 203

Synchronization in Multiple-mainframe Measurements
A TTL Trigger line between VT1433Bs making group measurements keeps all
modules synchronized. This is an open-collector line where each module holds
the one designated as the SYNC line low until the module is ready to advance to
the next measurement state. Another TTL Trigger line is designated to carry the
sample clock to all modules. This shared sample clock may come from any
VT1433B module in Mainframe A or from an external signal routed through the
Slot 0 Commander in Mainframe A.
One module is responsible for pulling the SYNC line low to start each group’s
state transition. Then, each module holds the line low until it is ready. When all
modules are ready, the SYNC line drifts high. The unidirectional line prevents
modules in Mainframe B from holding-off modules in Mainframe A.
The lowest logical address must be in Mainframe A because of VXI-MXI and
Resource Manager (RM) constraints. Group constraints with the C-Library force
modules in Mainframe A to have their FIFOs emptied last. The C-Library reads
data in channel order, so the highest channel is read last. To get this to work
automatically, the call to e1432_assign_channels() must list the logical addresses
in descending order.
Channel triggering must be done only by modules in Mainframe A. A trigger in
any other mainframe would not be communicated back on the SYNC line to
Mainframe A. The C-Library itself selects the VT1433B with the highest channel
number for synchronization.
VXI-MXI Module Setup and System Configuration
To set up a multiple mainframe system, follow the “Hardware Installation Rules”
which appear in Chapter 2 of the Agilent/HP E1482B VXI-MXI Bus Extender
User’s Manual. This allows the Resource Manager to configure the system.
The VXI-MXI Module setup in Mainframe A needs to be changed from those set
by the factory. The VXI-MXI module is not the Slot 0 Controller for
Mainframe A. See Table 2-1. Configuration Settings in the Agilent/HP E1482B
VXI-MXI Bus Extender User’s Manual. This requires changing several switch
settings.
q
Set the module as not being the Slot 0 Controller.
q
Set the VME timeout to 200 µ s.
q
Set the VME BTO chain position to 1 extender, non-slot0.
q
Do not source CLK10.
q
Set the proper logical address.
VT1433B User's Guide
The Host Interface Library
4-17