VTI Instruments EX1000A, User Manual

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VTI Instruments Corp.
64 EX10xxA Triggering
information, and as a general purpose output device. The digital I/O connector is a standard DB-9
with the following pin assignment:
Pin Function
1 DIO Channel 0
2 DIO Channel 1
3 DIO Channel 2
4 DIO Channel 3
5 DIO Channel 4
6 DIO Channel 5
7 DIO Channel 6
8 DIO Channel 7
9 GND
1 2 3 4 5
6 7 8 9
T
ABLE
3-7: D
IGITAL
I/O C
ONNECTOR
& P
IN
A
SSIGNMENT
As a general purpose output device, each DIO channel can be independently programmed with
regards to its output functionality and its static level to assume when enabled as an output. When
not enabled as an output, a channel becomes tri-stated, preventing conflict with other potential
voltage drivers. Reference the port’s electrical specifications in Table 3-8 for voltage tolerance
limits and output drive capabilities. Regardless of output functionality, each channel provides
constant input functionality. That is, the input level on each channel can be accessed without a
specific enable function call. Moreover, the base functionality of the DIO channels is not affected
by triggering, scanning, or any other instrument process. Unless linked to a limit condition, as
discussed below, its operation is completely autonomous.
When enabled as an output, each channel also has the ability to generate a 1 µs pulse upon command.
An example application of this pulse is to use the EX10xxA to externally trigger another piece of
test equipment. The specific operation of the pulse depends on the static level programmed for that
channel. When a channel is programmed with a static level of high, the pulse will be low-going.
When a channel is programmed with a static level of low, the pulse will be high-going. Each pulse
generation requires a separate function call.
For expanded and more automated operation, each DIO channel can be independently linked to one
or multiple limit conditions on one or more input channels. This is termed a DIO Limit Event. For
example, DIO channel 0 can be programmed to go high when the upper limit of set 0 for channel 2
or the lower limit of set 1 for channel 1 is exceeded. When linked as a limit event, a DIO channel
will be cleared at the beginning of a new acquisition. Its state will then be updated with each scan
according to the programmed limit evaluations. By default, the cleared state is low, but can be set
on a per channel basis to be high through the use of the Invert setting. Similarly, the default operation
of each channel is non-latch mode, but can be set on a per channel basis to be latch mode. In latch
mode, a transition out of the cleared state would remain, regardless of future limit evaluations, until
it is cleared at the beginning of a new acquisition.
It is important to note that the control of the DIO channels through DIO Limit Event assignment
does not lock out control through the direct output mechanism. For example, even if a DIO channel
has been set high by a DIO Limit Event, it could be asynchronously set low through direct output
control. Because limits can only be evaluated as fast as data is being acquired, there could be an
application that employs a slow sampling rate but requires the DIO channel to be reset sooner than
the normal limit evaluation mechanism would do it. The direct DIO control provides this capability.
Use of that control does not alter or disable the limit event mechanism controls; it simply
asynchronously alters the level of the DIO channel output. Upon the next scan (and subsequent limit
evaluation), the DIO channel will be updated normally per its DIO Limit Event configuration. In
general, however, an application will employ only one control mechanism. For that reason, if a DIO