Measurement Computing USB-1608FS-Plus - Manual (Page 13)

USB-1608FS-Plus User's Guide Functional Details
13
6. Replace the top section of the housing, and fasten it to the bottom section with the three screws.
For more information on digital signal connections
For general information regarding digital signal connections and digital I/O techniques, refer to the Guide to
Signal Connections (available on our web site at
www.mccdaq.com/signals/signals.pdf ).
Counter input
The CTR terminal is a 32-bit event counter that can accept frequency inputs up to 1 MHz. The internal counter
increments when the TTL levels transition from low to high.
SYNC I/O
The SYNC terminal is a bidirectional I/O signal that can be configured as an input (default) or an output.
 Configure as an external clock input to pace the A/D conversions from an external source. The SYNC
terminal supports TTL-level input signals of up to 100 kHz.
 Configure as an output that may be used to pace conversions on a second device and acquire data from
16 channels. Refer to page 15 for more information about synchronized operations.
Trigger input
The TRIG_IN terminal is an external digital trigger input. The trigger mode is software-selectable for edge or
level sensitive. Edge sensitive mode is selectable for rising or falling. Level sensitive mode is selectable for
high or low.
Reserved
The RSVD terminal is reserved for future use.
Ground
The analog ground ( AGND ) terminals provide a common ground for all analog channels.
The digital ground ( GND ) terminals provide a common ground for the digital, trigger, counter, and sync
channels and the power terminal.
Power output
The PC +5V output terminal can output up to 200 mA maximum. You can use this terminal to supply power to
external devices or circuitry.
Caution! The PC +5V terminal is an output. Do not connect it to an external power supply or you may
damage the device and possibly the computer.
The maximum output current that can be drawn by the USB-1608FS-Plus is 500 mA. This maximum applies to
most personal computers and self-powered USB hubs. Bus-powered hubs and notebook computers may limit
the maximum available output current to 100 mA. If the current requirement of the device exceeds the current
available from the computer, connect to a self-powered hub or power the computer with an external power
adapter.
When running applications with the device, each DIO bit can source up to 24 mA. The total amount of current
that can be sourced from the PC +5V, SYNC, and digital outputs is 200 mA max.
Accuracy
The overall accuracy of any instrument is limited by the error components within the system. Resolution is
often used incorrectly to quantify the performance of a measurement product. While "16-bits" or "1 part in
65,536" does indicate what can be resolved, it provides little insight into the quality, or accuracy, of an absolute
measurement. Accuracy specifications describe the actual measurement achievable with a USB-1608FS-Plus.
Accuracy specifications are listed on page 17.