Ttl Output Modes - Newport 6100 User Manual

130 Principles of Operation
The Modulation Input can be turned off from the LDD Params menu, to
reduce the picked up noise from its BNC connector, when the laser current is
not modulated (see 4.4.9.1).
6.4.2.4 Photodiode Input and Bias Adjustment
A monitor photodiode may be reverse biased up to -5 volts using the
PD BIAS adjustment screw. In the farthest counter-clockwise position the
photodiode is zero biased. Turning the screw clockwise increases the bias
voltage.
6.5

TTL Output Modes

The TTL Output signal on the rear panel SIGNALS I/O connector allows the
user to monitor certain states of the Model 6100, or to control or trigger
external measurement equipment. This output operates one of five modes –
LOW, HIGH, ENABLE OUTPUT MONITOR, PULSE MONITOR, and
TTL INPUT MONITOR.
Following power-up, the unit always will be in ENABLE OUTPUT
MONITOR TTL output mode. The user may then change to one of the other
TTL output modes using the LAS:TTL:MODE command via the USB
interface. See Section 5.5 for more information on this command. It is not
possible to change the operating mode from the front panel of the unit.
Operating mode is not retained in the unit at power down.
6.5.1 LOW TTL Mode
In LOW TTL mode, the open-collector output pulls the TTL Output signal to
Digital Ground.
6.5.2 HIGH TTL Mode
In HIGH TTL mode, the open-collector output is floated and the 1.5 kohm
resistor pulls the TTL Output signal to +5V.
6.5.3 ENABLE OUTPUT MONITOR TTL Mode
In ENABLE OUTPUT MONITOR TTL mode, the TTL Output signal
indicates when the Laser Diode Driver subsystem is outputting current or is
capable of doing so without the normal 3-second safety delay.
Normally, the TTL Output signal will be HIGH when the unit is supplying
current to a laser diode and LOW when the unit is not. There are two
exceptions to this. One exception is when output current is enabled, but it is
blocked because the unit is between pulses in GATED, TRIGGERED,
RETRIG, and FREE RUN pulse modes. The other exception is when output
current is enabled but the unit is in EXTERNAL ANALOG CONTROL
operating mode and the Analog Control input signal on the rear-panel IO