Teledyne LeCroy Detective - Users Manual - Manual (Page 8)

CATC CATC Detective User’s Manual Version 2.21
Page 5
“External Start” or the “External Stop” recording mode. Once one of these recording modes has
begun, the analyzer waits for an external trigger signal to either start or end the recording session.
Manually pushing the TRIG button will assert the external trigger signal and thus affect the
operation.
Note: Early versions of the Detective USB Probe have either two A-type USB connectors or two
A-type USB connectors and one B-type USB connector.
Note: Early versions of the USB Detective Probe have a 2
×
2 pin header instead of the 5
×
2 pin
header. This header carries the same TRIG signal described above. The 2
×
2 triggering
header signals pin assignment is illustrated below:
GND
TRIG
GND
TRIG
2.4.1 External Triggers
The CATC Detective Probe offers two ways to generate an external trigger to control a recording
session: the “Manual Trigger” push-button, and the “TRG” pin in the Probe Triggering Header.
2.4.1.1 The Manual Trigger Push-Button
The simplest way to generate an external trigger (when enabled in the Recording Options dialog
box) is by manually activating the Manual Trigger push button located on top of the Probe.
2.4.1.2 TRG Signal Generation
In order to view a particular USB event (to determine—for example—how a particular device
behaves during the initialization phase), it is necessary to activate the CATC Detective analyzer
to record the bus activities during a specific time period. If the USB host allows manual control
of the bus traffic, then in theory the CATC Detective recording could be started manually at the
same time. Because of USB speed, correspondingly slow human reaction time, and buffer
memory limitations (1 Mbytes), however, manually coordinating the host actions with the
Detective recording is generally impractical.
A simple solution is to generate a signal in the USB host PC, or in the USB hub or device under
observation, that will be synchronized to the particular event to be recorded. Such a signal can be
generated on the PC by calling a small software routine (see sample code below) that uses a
standard I/O Write command to a specific pin on an available serial or parallel port.
Alternatively, the TRG signal might be generated by programming one of the general I/O ports
on the USB controller in the hub or device.
A short cable connects this (active low) signal to the TRG pin of the Probe Triggering Header.