|
SIM (Small Instrumentation Modules) is a robust, flexible platform
in which up to eight high performance instruments share the same
compact mainframe and computer interface. Unlike other modular
systems, both front-panel and computer operation are possible. With
SIM you get the functionality you need while avoiding the cost of
unnecessary features. You configure your own system from a broad
and growing selection of modules.
The SIM900 Mainframe is the platform on which a SIM system is assembled.
The mainframe provides power, computer interfaces, clock synchronization,
and individual module status. Eight internal module slots accommodate
single-width and double-width modules. For the occasional application
needing a module right next to an experiment, a rear-panel connector
and an interconnect cable permit operation of a 9th
module outside the mainframe.
Communications
The mainframe comes with a standard RS-232 host interface and GPIB
(IEEE-488.2) as an option. All commands and queries to individual
modules are routed through the mainframe host interface. Messages
are routed based on their port number, with the mainframe seamlessly
relaying data to and from the appropriate destination. This messaging
system is also used to communicate through the two auxiliary RS-232
ports. Using these ports, any number of SIM900 mainframes and other
RS-232 instruments may be controlled through one host interface
in the master mainframe.
Each port in the mainframe has independent 511-byte input and output
queues. The mainframe also performs any rate adaptation needed when
communicating through the ports. A dedicated "eavesdrop"
RS-232 port provides an echo of all communications to and from the
mainframe to ease debugging of new setups.
Timebase
The mainframe provides a master 10 MHz clock to the modules which
lock their internal timebases to this reference. The master clock
in the SIM900 can be either free-running or phase-locked to an external
10 MHz reference through a rear-panel BNC input.
Start-Up Script
A 4000 byte start-up script is maintained in non-volatile memory
in the SIM900. When enabled, the commands stored in the script are
executed each time the mainframe is turned on. This provides a simple
way to ensure all modules are automatically set to a desired starting
configuration.
Front Panel
Front-panel LED indicators provide status information for the mainframe
and also monitor communications between the host and installed modules.
Indicators display host interface, timebase, communications status,
start-up script, and power information.
Power Supplies
All modules operate from various combinations of ±5 V, ±15
V and +24 V. These well regulated and filtered DC voltages are supplied
by the mainframe power supply which is forced air cooled to maintain
stable performance. All supplies are current limited with a trip-off
circuit in case of an over voltage or short circuit.
|
