9.2 Event Inputs 61
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.
The bottom number is the standard deviation (sigma) of the values of the 16 samples.
9.2.8 RS-232C Event Trapping
The event capture channel of the Model 1092A/B/C and 1093A/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.
9.2.9 Event Trapping Setup
Configuring the clock to trap events on the RS-232C interface requires making the configuration
changes described in Section 5.3.4.
Arm the Event-Trapping circuit from the front panel using the SET RS-232 sub-menu of the
SETUP menu. 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:
Press the following keys in order; SETUP > ENTER > SETUP > SETUP. The display should
indicate the following:
SET A EVENT?
Press ENTER again and the display should indicate the following:
ARM A EVENT?
PRESS ENTER TO ARM
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, either by 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 10.2.4.
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