Measurement Computing TempScan/1100 - Manual (Page 72)

4-14 System Configuration 879596 TempScan / MultiScan User's Manual
If the Pre-Trigger pre is set to a non-zero value, the TempScan/1100 or MultiScan/1200 will begin
sampling Pre-Trigger data immediately after the Set Trigger Configuration ( T ) command is issued, at the
rate specified by the current normal scan interval, as set via the Set Scan Interval ( I) command.
When the Trigger start event occurs, the Pre-Trigger data portion of the Trigger Block will contain the
most recent Pre-Trigger scans. The number of Pre-Trigger scans collected will depend upon when the
Trigger occurs. If the Trigger occurs when the number of acquired Pre-Trigger scans is less than the
specified Pre-Trigger
pre , then that number of Pre-Trigger scans will be the number of Pre-Trigger scans
collected to that point. Otherwise, if the Trigger occurs when the number of acquired Pre-Trigger scans is
greater than the specified Pre-Trigger
pre , then the number of Pre-Trigger scans will be the number
specified by the Pre-Trigger pre parameter of the Set Counts ( Y ) command. If no acquisition data is
desired while in the Pre-Trigger state, the Pre-Trigger pre parameter of the Set Counts ( Y ) command may
be set to zero.
Pre-Trigger data may not be accessed while the TempScan/1100 or MultiScan/1200 unit is in the Pre-
Trigger state. The Pre-Trigger data for a particular Trigger Block is not made available to be read until the
specified Trigger occurs. There are two ways to determine if the unit is in the Pre-Trigger state:
• Check the TempScan/1100 or MultiScan/1200 front panel. If the TRIGGER LED indicator is flashing,
then the unit is in the Pre-Trigger state.
• Query the Status Byte Register (
STB ) via the User Status ( U1 ) command. If the acquisition has been
configured and the Triggered Bit (Bit 1) is not set , then the unit is in the Pre-Trigger state. When the
specified Trigger occurs, the TempScan/1100 or MultiScan/1200 exits the Pre-Trigger state and enters
the Post-Trigger state.
Post-Trigger State
The Post-Trigger state is the acquisition period after the Trigger (trigger start event) and before the Stop
(trigger stop event). While the unit is in this state, the TRIGGER LED indicator will be on. As in any
other acquisition state, the alarms and their associated outputs will be updated as follows: At the fastest rate
possible under the current channel configuration, for the TempScan/1100; and at any programmed Post-
Trigger scan rate up to the fastest rate possible under the current channel configuration, for the
MultiScan/1200.
During this state, the unit will collect Post-Trigger data at the rate specified by the acquisition scan
interval, as set via the Set Scan Interval (
I ) command. Post-Trigger scans will be collected at this rate
until the Stop event occurs. The number of scans collected during the Post-Trigger state is not restricted
by the internal buffer size. The TempScan/1100 or MultiScan/1200 can collect scans in the Post-Trigger
state indefinitely, if the controlling computer is capable of reading data out of the Acquisition Buffer fast
enough to prevent a buffer overrun.
The Post-Trigger state may be detected by doing the following: Querying the Triggered Bit (Bit 1) of the
Status Byte Register (
STB ) via the User Status ( U1 ) command; and querying the Stop Event Bit (Bit 1) of
the Event Status Register ( ESR ) via the User Status ( U0 ) command. If and only if the Triggered Bit (Bit 1)
of the STB is set, and the Stop Event Bit (Bit 1) of the ESR is not set, then the TempScan/1100 or
MultiScan/1200 unit is in the Post-Trigger state. The unit will exit the Post-Trigger state when the Stop
event occurs.
Post-Stop State
The Post-Trigger state is the acquisition period after the Stop (trigger stop event) until the completion of
the acquisition. While the unit is in this state, the TRIGGER LED indicator will be on. As in any other
acquisition state, the alarms and their associated outputs will be updated as follows: At the fastest rate
possible under the current channel configuration, for the TempScan/1100; and at any programmed Post-
Stop scan rate up to the fastest rate possible under the current channel configuration, for the
MultiScan/1200.