Caen ELS PreDAC, User Manual

Page: 19 / 52

PreDAC User’s Manual
19
2.2.2 TRG Command
The TRG Command enables to synchronize the PreDAC output voltage setting
to an external event via the hardware “Trigger/Gate” signal (refer to the Triggers
Connector section). This feature is extremely useful when the digital to analog
converter must be synchronized to an external event (e.g. an experimental time window
or a machine specific frequency).
In the
normal mode the execution of the SET command reflects in the
immediate change of the output voltage value. In the trigger mode , on the other hand,
the execution of the SET command does not get into operation immediately. The output
voltage value which is set with the SET commands is saved into memory (on a
temporary register): when the external signal occurs it forces the change of the output
voltage setting. The
trigger mode operation is hereafter described.
As soon as the “TRG:ON \r\n
” command is received the PreDAC unit replies
with an acknowledgement string (“ACK \r\n
”) and enters the
trigger mode . When
entering this mode, the unit waits for a rising edge (positive edge) on the corresponding
“Trigger/Gate” input signal. As soon as this event is detected by the PreDAC unit, the
internal logic transfers the output voltage value from the temporary register to the
output register which results in the output voltage update on the BNC output connectors.
This behavior is kept until the
trigger mode is disabled with the “TRG:OFF \r\n
”
( default ) command. Please note that an acknowledgment string is sent back to the host
after a “TRG:ON \r\n
” or “TRG:OFF
\r\n
” command is received.
User can set different output voltages on various channels with different SET
commands corresponding to voltage setting on each channel and then update them
simultaneously as soon as the external trigger pulse is received (see the example below).
Each subsequent write to the channel temporary register overwrites the previous value,
so only the last written and stored value is fed to the output register and thus to the
output connector.
To read the actual trigger mode status it is possible to use the command:
“TRG:?
\r\n
”. The generated reply to this command has the next form: “TRG:ON
\r\n
”
when the “trigger mode” is enabled or “TRG:OFF
\r\n
” when the
trigger mode is
disabled.
Example:
TRG example:
TRG:ON \r\n
ACK \r\n
(pause)