VTI Instruments EX1401, User Manual

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EX1401 Basic Operation 43
information, and as a general purpose input/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
3-5: 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 logic state, when enabled as an output. When not enabled
as an output, a channel becomes tri-stated, preventing conflict with other potential voltage drivers.
Refer the port’s electrical specifications 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. It is also possible
for the DIO data to be acquired and reported along with the analog channel data. Unless linked to a
limit condition, as discussed below, the DIO port’s operation is completely autonomous.
The default selections for each DIO channel are:
•
output enable is off
•
output level is 0
The electrical specifications for the digital I/O port are provided in EX1401 Specifications.
The Digital IO port is bank isolated from chassis ground/earth potential for up to ±250VPEAK.
However, there is no inter-channel isolation between digital channels. The Digital I/O port is ESD
protected on all IO pins. Use a shielded cable when connecting to the Digital IO port for CE.
NOTE Each Input channel of Digital IO port is pulled down through 10K Ohm resistor to its ground
T
RIGGERING
The EX1401 supports a full function trigger model with a separate arm source and trigger source
event structure. For a complete explanation of the trigger model, see Start, Arm, Trigger, and Alarm
in Section 5. In summary, an acquisition sequence is enabled with a trigger initialize command.
Scanning is then initiated upon the receipt of the programmed arm source event followed by the
receipt of the programmed trigger source event. Trigger and arm source events can be independently
programmed from a variety of sources including Immediate, Software, External trigger, Digital I/O,
LAN Events, and LXI alarms.
D
ATA
F
ORMAT
By default, the data returned during data retrieval is limited to the channel readings and the absolute
time of measurement initiation. If enabled, the EX1401 can also return the measured CJC
temperatures.