Measurement Computing USB-1616FS - Manual (Page 17)

USB-1616FS User's Guide Functional Details
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SYNC I/O
The SYNC terminal is a bidirectional I/O signal that can be configured as an input or an output:
 Configure as an external clock input to externally clock the A/D conversions. The SYNC terminal supports
TTL-level input signals.
 Configure as an output to synchronize with a second USB-1616FS and acquire data from 32 channels. For
more information about synchronized operations see page 20.
Power output
The +5V terminal (labeled 5V ) draws power from either the USB connector VBUS terminal or the external
power supply.
Caution! The +5V terminal is an output. Do not connect to an external power supply or you may damage
the USB-1616FS and possibly the computer.
The maximum amount of +5 V current from the +5 V terminal is limited to 50 mA.
Ground terminals
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, sync and power
terminals.
Daisy chaining additional devices to the USB-1616FS
Daisy chained MCC USB Series products connect to the USB bus through the high-speed hub on the USB-
1616FS. You can daisy chain a maximum of four MCC USB Series products to a single USB 2.0 port on your
computer, or a maximum of two devices to a single USB 1.1 port. Use the supplied cable or an equivalent cable
for daisy chaining to additional MCC USB Series products.
MCC USB Series products are USB 2.0 full-speed devices that provide a signaling bit rate of 12 Mb/s. The
throughput rate is shared by all devices connected to the USB bus.
Complete the following steps to daisy-chain two or more USB-1616FS devices. This procedure assumes you
already have one USB-1616FS connected to a computer and to the external power source. The USB-1616FS
already connected to the computer is referred to as the connected device. The USB-1616FS you want to daisy-
chain to the connected device is referred to as the new device.
1. Connect the Power OUT connector on the connected device to the POWER IN connector on the new
device.
2. Connect the USB OUT connector on the connected device to the USB IN connector on the new device.
3. For each additional device you want to add, repeat steps 1-2, with the device you just daisy chained now
being the connected device.
Sample rate limitations when using multiple USB-1616FS devices
The maximum sample rate when using multiple USB-1616FS boards is system-dependent. Multiple board
performance is limited by an overall aggregate sample rate. The maximum throughput is in number of samples
taken per second. The rate is irrespective of the number of channels sampled or the number of boards installed.
The maximum sample rate of any one channel is limited to 50 KS/s.
The typical limiting factor for throughput is CPU usage. At maximum system throughput, virtually all available
CPU power is consumed by the USB data transfer. When you run your system close to its maximum
throughput, the amount of CPU power that is available for running other concurrent processes is limited.
Benchmark performance rates are listed in the Specifications chapter on page 23.