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Appendix C
E
VENT
T
IME
-T
AGGING
O
PTION
C.1
Introduction
General Description & Specification
TCG 01’s Event Time-Tagging Option provides for the time-stamping of rising edges
seen at either channel of P6. This is a TTL level input with an input burden of 7mA.
Event time is deemed to be the rising edge of a pulse. The minimum pulse duration is
1us, and the maximum rate of time tag recording is 100 tags per second (aggregated
over both inputs). In the event of pulses occurring simultaneously on both inputs, both
events are captured and recorded independently with the same time data.
Tag Data
Time Tags use UTC time, and each tag includes the year, day of year, hour, minute and
second, as well as fraction of second to a resolution and accuracy of 100ns. TCG 01
measures time internally in 40ns intervals, rounding to the nearest 100ns for time tag
storage purposes, thus allowing accuracy to equate to resolution. Each tag record
includes the input channel number, as well as the clock sync status as at the tag time.
Tag Storage
TCG 01 stores Time Tags in a data queue designed as a circular buffer. The maximum
number of time tags that may be stored is 512. If further events occur when the buffer is
full, TCG 01 sets an overflow status and continues storing tags, overwriting the oldest
data first.
Tag Retrieval
The user can retrieve time tags from the buffer using a request/response protocol
operating over TCG 01’s serial port interface. Tags are retrieved from the buffer - oldest
data first.
TCG 01 can be configured to broadcast either status or serial time strings over the serial
port. Most users of the time tag option will want to suppress all broadcast outputs to
simplify the task of time tag data collection. However, if output strings
are
programmed,
then TCG 01 will still output time tag information when requested, timing the responses
to avoid interference with the other traffic on the port.
