Communications Examples for SIMs
The Small Instrumentation Module family was designed to support simple communications between a
user's computer and a collection of instruments. While it is possible to communicate directly with a
SIM module, this note will only consider the case of communication through a SIM900 Mainframe.
The SIM900 has two host computer interfaces, RS-232 and GPIB, one of which is active. To switch
interfaces, use the rear-panel piano-style DIP switch (position 3): up is for RS-232, down is for GPIB.
The 5 right-most switches are interpreted based on the host selection, and determine either default
baud rate (RS-232) or instrument address (GPIB). Only one host interface can be active, and the
selection is determined at power-on time for the SIM900.
The simplest style of communication through the SIM900 is the "connection" model, where a single
bidirectional I/O stream is managed. Upon power-on, this stream is i|