VTI Instruments EX1000A User Manual page 66

VTI Instruments Corp.
For proper operation, each trigger bus connector must be populated with either a cable or a
termination. Since the two connectors per unit are in parallel, they are electrically equivalent with
respect to receiving the cable or termination. VTI Instruments P/N: 70-0304-000 provides two
termination assemblies, which is sufficient to connect any number of instruments, since a
termination is only needed at each end. An example of a three-unit trigger bus installation is shown
in Figure 3-1.
As a general purpose output device, each VTB 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. 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 VTB channels is not affected by triggering,
scanning, or any other instrument process.
When enabled as an output, each channel also has the ability to generate a 1 µs pulse upon command.
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.
A common application of the pulse generation is multiple-unit synchronization. Referring to
Figure 3-1 above, each unit can be configured to trigger on the same VTB channel. Then one unit
is selected as a master and is used to output a signal on the designated VTB channel line, serving as
a common trigger source for all three instruments.
The default selections for each VTB channel are:

output enable is off

output level is 0
The electrical specifications for the trigger bus are provided in Table 3-10.
66
Trigger Bus
Terminators
F 3-1: T
IGURE RIGGER
Characteristic
Logic Type
V
IT+
V
IT-
V
OS
T 3-10: T B
ABLE RIGGER US
B C E
US ABLING XAMPLE
Value
M-LVDS Type 2
150 mV max
50 mV min
1 V typical
E S
LECTRICAL PECIFICATIONS
EX10xxA Triggering