Measurement Computing USB-1408FS - Manual (Page 14)

USB-1408FS User's Guide Functional Details
14
Channel gain queue
The channel gain queue feature allows you to set up a scan sequence with a unique per-channel gain setting and
channel sequence. The gain settings are stored in a channel-gain queue list that is written to local memory on
the device.
The channel-gain queue list can contain up to 16 elements in any order. An example of a four-element list is
shown in the table below.
Sample channel gain queue list
Element Channel Range
0 CH0 BIP10V
1 CH3 BIP5V
2 CH1 BIP10V
3 CH2 BIP1V
When a scan begins with the gain queue enabled, the USB-1408FS reads the first element, sets the appropriate
channel number and range, and then acquires a sample. The properties of the next element are then retrieved,
and another sample is acquired. This sequence continues until all elements in the gain queue have been selected.
When the end of the channel list is detected, the sequence returns to the first element in the list. This sequence
repeats until the specified number of samples is acquired.
Carefully match the gain to the expected voltage range on the associated channel or an over range condition
may occur. Although this condition does not damage the device, it does produce a useless full-scale reading,
and can introduce a long recovery time due to saturation of the input channel.
Analog output
You can connect up to two analog output connections to D/A OUT 0 and D/A OUT 1 . Each channel can be paced
individually at rates up to 10,000 updates per second. Both channels can be paced simultaneously using the
same time base at 5,000 updates per channel. The 0 V to 4.096 V output range provides a convenient 1 mV per
LSB when setting the output voltage levels.
Digital I/O
The device has 16 digital bits configured as two 8-bit ports (Port A and Port B). You can connect up to eight
digital I/O lines to each port (terminals
Port A0 to Port A7 and Port B0 to Port B7 ). Each port is configurable
as either input or output.
When configured for input, you can use the digital I/O terminals to detect the state of any TTL level input.
Refer to the schematic shown in Figure 8. If the switch is set to the +5 V input, Port A0 reads TRUE (1). If you
move the switch to GND, Port A0 reads FALSE.
Figure 8. Schematic showing switch detection by digital channel Port A0
Pull-up/down configuration
Later hardware revisions are designed with user-configurable internal jumpers to configure the digital bits for
pull-up (default) or pull-down. If the p/n of your board is 195920B, the default configuration is pull-up. To
configure for pull-down, the board must be modified at the factory. If the p/n of your board is 193331x, where x
is any letter, your board has the user-configurable internal jumpers. The hardware revision is listed with the part
number on the bottom of the device, for example p/n 193331D.