BNC 725 - Manual (Page 14)

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Lock/Unlock Panel
Lock or unlock the front panel buttons using the Lock Panel and Unlock Panel buttons. This
functionality is handy, for example, in an embedded control application where the Model 725
should function only in stand-alone or computer-controlled modes. When the panel is locked, the
LED next to the power button glows a steady red and all buttons are dark. When the panel is
unlocked, the power LED glows green and the front-panel buttons are illuminated.
Like the enable/disable I/O functions, these settings are nonvolatile and are restored on power up.
Because the power button is disabled, the Model 725 must be disconnected from AC power to
turn it off, if the front panel is locked.
Time base settings
Each pair of channels of the Model 725 can independently utilize one of four different time bases
so you can control and measure events which occur a few nanoseconds apart, or a few hundred
seconds apart.
In 100 MHz time base mode (the default), the Model 725 aligns signals to an internal 100 MHz
clock, for timing resolution of 10 ns. Use this “high resolution” mode when the events of your
experiment occur in rapid succession (milliseconds or less).
100/64 MHz time base mode allows the Model 725 to control events that occur over longer time
periods (milliseconds to minutes). This is called “low resolution” mode in the following
documentation.
In Ext. time base mode, the channels use an external clock input for the time base. This input
must be TTL-level between 1 and 100 MHz applied to the External Clock (ext clk) input on the
back of the Model 725. This function allows the use of high-precision or variable-frequency time
bases. It also allows multiple Model 725s to be synchronized to the same base.
The External time base cannot be produced by a channel that uses the same time base as an input.
Ext./64 time base mode divides the frequency of the signal applied to the external clock input
before using it as a time base. If the external clock is being used as a time base, the frequency
entered into the edit box is used to calculate the timing settings. If this setting is 10% higher than
actual, the channels using this time base will be 10% long on delays and duration.
NOTE: When you change the time base setting a warning may appear listing
channels for which the clock range settings are invalid. The software will go into
“offline” mode allowing you to adjust the timing settings for the listed channels.
Once you’ve done so, go “online” and click Program > Program all channels.