Measurement Computing USB-1208LS - Manual (Page 13)

USB-1208LS User's Guide Functional Details
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Since the analog inputs are restricted to a −10 V to +20 V signal swing with respect to ground, all ranges except
±20V can realize a linear output for any differential signal with zero common mode voltage and full scale signal
inputs. The ±20 V range is the exception. You cannot put −20 V on CHHI and 0 V on CHLO since this violates
the input range criteria.
The table below shows some possible inputs and the expected results.
Sample Inputs and Differential Results
CHHI CHLO Result
–20 V 0 V Invalid
–15 V +5 V Invalid
–10 V 0 V –10 V
–10 V +10 V –20 V
0 V +10 V –10 V
0 V +20 V –20 V
+10 V –10 V +20 V
+10 V 0 V +10 V
+15 V –5 V +20 V
+20 V 0 +20 V
For more information on analog signal connections
For more information on single-ended and differential inputs, refer to the Guide to DAQ Signal Connections
(this document is available on our web site at
www.mccdaq.com/signals/signals.pdf .)
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 8 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 CH0 BIP5V
2 CH3 BIP10V
3 CH2 BIP1V
When a scan begins with the gain queue enabled, the USB-1208LS 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.
Digital I/O
You can connect up to 16 digital I/O lines to the screw terminal containing pins 21 to 40 ( Port A0 to Port A7 ,
and Port B0 to Port B7 .) You can configure each digital port for either input or output.
When you configure the digital bits for input, you can use the digital I/O terminals to detect the state of any
TTL level input.