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© National Instruments Corporation 6-1 PC-OPDIO-16 User Manual
Chapter 6
NI-DAQ Function Reference
This chapter contains important information about how to apply the NI-DAQ function
descriptions in this manual to your programming language and environment. This chapter also
includes a detailed description of each NI-DAQ function that supports the PC-OPDIO-16. You
can skip this chapter if you are an experienced NI-DAQ user.
Using NI-DAQ Functions
Status Codes
Every NI-DAQ function is of the following form:
status = Function_Name (parameter 1, parameter 2, parameter n)
where n = 0. Each function returns a value in the status variable that indicates the success or
failure of the function, as shown in Table 6-1.
Table 6-1. Status Values
Status Result
Negative Function did not execute because of an error
Zero Function completed successfully
Positive Function executed but with a potentially serious side effect
In DOS and Windows, status is a 2-byte integer.
Variable Data Types
The NI-DAQ Application Programming Interface (API) is almost identical in DOS and
Windows, except for some of the parameter data types. Every function description has a
parameter table that lists the data types in each of the environments. LabWindows uses the same
types as DOS, and LabWindows/CVI uses the same types as Windows. The following sections
describe the notation used in those parameter tables and throughout the manual for variable data
types.