Introduction

Whether you are using RS-232, GPIB, Ethernet, VXI, or USB, message-based communication is a standard protocol for controlling and receiving data from instruments. Because most message-based devices have similar capabilities, it is natural that the driver interface should be consistent. Under VISA, controlling message-based devices is the same regardless of what hardware interface(s) those devices support or how those devices are connected to your computer.

VISA message-based communication includes the Basic I/O Services and the Formatted I/O Services from within the VISA Instrument Control Resource (INSTR). All sessions to a VISA Instrument Control Resource (INSTR) opened using viOpen() have full message-based communication capabilities. Of course, if the device is a register-based VXI device, the message-based operations return an error code (VI_ERROR_NSUP_OPER) to indicate that this device does not support the operations, although the session still provides access to them. This help file discusses the uses of the Basic I/O Services and the Formatted I/O Services provided by the INSTR Resource in a VISA application.