Measurement Computing USB-3102 - Manual (Page 18)

USB-3102 User's Guide Functional Details
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Synchronous DAC load terminal (SYNCLD)
The synchronous DAC load connection (pin 49) is a bidirectional I/O signal that allows you to simultaneously
update the DAC outputs on multiple devices. You can use this pin for two purposes:
 Configure as an input (slave mode) to receive the D/A LOAD signal from an external source.
When the SYNCLD pin receives the trigger signal, the analog outputs are updated simultaneously.
SYNCLD pin must be logic low in slave mode for immediate update of DAC outputs
When the SYNCLD pin is in slave mode, the analog outputs can be updated immediately or when a positive
edge is seen on the SYNCLD pin (this is under software control.)
The SYNCLD pin must be at a low logic level for DAC outputs to update immediately. If the external source
supplying the D/A LOAD signal is pulling the SYNCLD pin high, no update will occur.
Refer to the "USB-3100 Series" section in the Universal Library User's Guide for information on how to update
DAC outputs immediately.
 Configure as an output (master mode) to send the internal D/A LOAD signal to the SYNCLD pin.
You can use the SYNCLD pin to synchronize with a second USB-3102 and simultaneously update the
DAC outputs on each device. Refer to
Synchronizing multiple units below.
Use InstaCal to configure the SYNCLD mode as master or slave. On power up and reset the SYNCLD pin is set
to slave mode (input).
Refer to the "USB-3100 Series" section in the Universal Library User's Guide for information on how to
configure the USB-3102 with the Universal Library.
Counter terminal (CTR)
The CTR connection (pin 52) is the input to the 32-bit event counter. The internal counter increments when the
TTL levels transition from low to high. The counter can count frequencies of up to 1 MHz.
Power terminal (+5V)
The +5 V connection (pin 56) draws power from the USB connector. This terminal is a +5V output.
Caution! The +5V terminal is an output. Do not connect to an external power supply or you may damage
the USB-3102 and possibly the computer.
Synchronizing multiple units
You can connect the SYNCLD terminal pin (pin 49) of two USB-3102 units together in a master/slave
configuration and simultaneously update the DAC outputs of both devices. Do the following.
1. Connect the SYNCLD pin of the master USB-3102 to the SYNCLD pin of the slave USB-3102.
2. Configure the SYNCLD pin on the slave device for input to receive the D/A LOAD signal from the master
device. Use InstaCal to set the direction of the SYNCLD pin.
3. Configure the SYNCLD pin on the master device for output to generate an output pulse on the SYNCLD
pin.
Set the Universal Library SIMULTANEOUS option for each device. Refer to the Universal Library User's Guide
for information on how to configure the USB-3102 with the Universal Library.