2.6.1 Channel Numbers

The LabJack U6 has 16 total built-in analog inputs. Two of these are connected internally (AIN14/AIN15), leaving 14 user accessible analog inputs (AIN0-AIN13). The first 4 analog inputs, AIN0-AIN3, appear both on the screw terminals and on the DB37 connector. There is about 4.4 kΩ of resistance between the duplicated connections, so connecting signals to both will not short-circuit the signals but they will contend with each other.

Table 2.6.1-1. Positive Channel Numbers

Table 2.6.1-2. Negative Channel Numbers

Channel 14 is not stream-able. The readings from the internal temperature sensor(channel 14) need extended settling time and this takes too long for stream-mode.

Channels 193 to 241 are special analog input channel numbers that read digital inputs, timers or counters.  See Section 3.2.1 for more information.

The Mux80 accessory uses multiplexer ICs to easily expand the total number of analog inputs available from 14 to 84, or you can connect multiplexer chips yourself.

The DB37 connector has 3 MIO lines (shared with CIO0-CIO2) designed to address expansion multiplexer ICs (integrated circuits), allowing for up to 112 total external analog inputs. The DG408 from Intersil is a recommended multiplexer, and a convenient ±12 volt power supply is available so the multiplexers can pass bipolar signals (see Vm+/Vm- discussion in Section 2.11). Figure 2-2 shows the typical connections for a pair of multiplexers.

To make use of external multiplexers, the user must be comfortable reading a simple schematic (such as Figure 2-2) and making basic connections on a solderless breadboard (such as the EB37). Initially, it is recommended to test the basic operation of the multiplexers without the MIO lines connected. Simply connect different voltages to NO0 and NO1, connect ADDA/ADDB/ADDC to GND, and the NO0 voltage should appear on COM.  Then connect ADDA to VS and the NO1 voltage should appear on COM.

If any of the AIN channel numbers passed to a U6 function are in the range 16-127 (extended channels), the MIO lines will automatically be set to output and the correct state while sampling that channel. For instance, a channel number of 28 will cause the MIO to be set to b100 and the ADC will sample AIN1. Channel number besides 16-127 will have no affect on the MIO. The extended channel number mapping is shown in Table 2-2.

For differential extended channels, the positive channel must map to an even channel from 0-12, and the negative channel must map to the odd channel 1 higher (i.e. 1-13).  That means that for extended channel numbers the negative channel must be 8 higher than the positive channel.  For example, a valid differential extended channel pair would be Ch+ = AIN70 and Ch- = AIN78, since AIN70 maps to AIN6 and AIN78 maps to AIN7.  For more information on differential extended channels, see the Mux80 Datasheet.

In command/response mode, after sampling an extended channel the MIO lines remain in that same condition until commanded differently by another extended channel or another function. When streaming with any extended channels, the MIO lines are all set to output-low for any non extended analog channels. For special channels (digital/timers/counters), the MIO are driven to unspecified states. Note that the StopStream can occur during any sample within a scan, so the MIO lines will wind up configured for any of the extended channels in the scan. If a stream does not have any extended channels, the MIO lines are not affected.

Table 2.6.1-3. Expanded Channel Mapping