62 Relay Contacts and Event Inputs
1. The top number is the mean (average) value of the most recent 16 records in the event buffer,
and represents the mean deviation (in microseconds) of the measured 1–PPS signal from the
GPS 1–PPS signal. A negative number means the applied 1–PPS signal is early, i.e. before
on-time, and a positive number means it is late, i.e. after on-time.
2. The bottom number is the standard deviation (sigma) of the values of the 16 samples.
8.2.8 RS-232C Event Trapping
The event capture channel of the Model 1084A/B/C can be configured to capture one or more
events via the RS-232C Serial Interface. The time mark for a captured event will correspond to
the leading edge of the start bit of the first character in the RS-232C signal. This event mode
can be both armed and interrogated for data over the RS-232C interface, allowing automated
synchronization of an external computer or system.
To perform event trapping via the RS-232C interface, the circuit must first be ARMED; that
is, made ready to receive an event trigger. Only one event may be captured after every arming,
but the events are stored sequentially in the event buffer in exactly the same manner as the normal
event time mode, thereby allowing up to 500 events to be recorded.
8.2.9 Event Trapping Setup
Configuring the clock to trap events (incoming data) on the RS-232C interface requires making the
configuration changes described in Section 5.2.2.
Arm the Event-Trapping circuit from the front panel using the SET RS-232 sub-menu from the
SETUP key. This menu also provides for configuration of communications port parameters (e.g.
baud rate, word length, etc.) to match those of the computer or equipment to be interfaced. The
following steps are required to arm the Event Trapping circuitry from the front panel:
1. Press the following keys in order; SETUP > ENTER > SETUP > SETUP. The display
should indicate the following:
SET A EVENT?
2. Press ENTER again and the display should indicate the following:
ARM A EVENT?
PRESS ENTER TO ARM
3. Press the ENTER button and the Event Input should be armed.
When the event occurs on the RS-232C port (i.e. the start bit of the next received character),
the event data can be reviewed in the event mode exactly as any normally captured event would
be. To capture further events, the circuit must be re-armed from the front panel or by using the
RS-232 Command “AR.”
Note that received commands are viewed as complete when the final character in the command
is received. Control characters, such as carriage-return and line-feed, are ignored and may follow
the “AR” command, but the start bit of the next character after the “R” (even if a carriage return)
may trigger the event timer. For a complete list of RS-232C Event Mode commands, refer to
Section 9.2.2.
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