Analog I/O Wildcard User Guide

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Selecting the Reference Voltage

The remaining jumpers on the Analog I/O Wildcard select the reference voltage for both the 12-bit DAC and the 16-bit A/D. These jumpers, referred to as the voltage reference selection jumpers, are labeled J3, J4, J5, and J6 and named "DAC Ref", "4V Ref", "5V Ref", and "Ref In/Out" respectively.

In most applications the DAC uses its own internal reference, and the jumpers J3, J4, and J5 select one of 3 reference voltages for the A/D converter (the DAC reference output, the 4.096V onboard reference, or the 5V reference, respectively). If installed, jumper J6 connects the A/D reference to pin 4 (VREF_PIN) on the Field Header.

The default configuration of the reference voltage selection jumpers is J4 and J6 installed. This connects the temperature-stable 4.096 reference voltage to the A/D reference input pin providing a 0 to 4.096 input range for each channel of the A/D. The default configuration also connects the 4.096 reference voltage to the reference pin on the Field Header (pin 4) for external connections. Using the default configuration requires that you initialize the DAC to generate its own reference voltage internally by passing the INT_1V_DAC12 or INT_2V_DAC12 parameters to the Init_Analog_IO function. This will allow the DAC to output voltages in the range of 0 to 2.048 volts or 0 to 4.096 volts respectively, as the maximum DAC output is twice the DAC reference voltage. The following sections describe the function of each jumper and list the valid jumper configuration options. CAUTION: Not all jumper configurations are valid and certain invalid configurations may damage the module.

DAC Reference Jumper

The DAC reference jumper, labeled J3, and named "DAC Ref" on the silkscreen of the Analog I/O Wildcard, connects the DAC reference pin to the A/D reference input pin. The DAC reference voltage can be generated internally, or supplied externally by installing jumper J6. The DAC reference voltage is configured with the function Init_Analog_IO and the constants INT_1V_DAC12, INT_2V_DAC12, or EXT_DAC12. Table 1-3 summaries the configuration options available for the DAC reference voltage with a jumper shunt installed across J3.

Table 1-3 DAC reference voltage configuration options with jumper J3 installed

4.096 Volt Reference Jumper

The 4.096 Reference Jumper, labeled J4, and named "4V Ref" on the silkscreen of the Analog I/O Wildcard, connects the onboard 4.096 voltage reference to the reference input pin on the A/D. This configures the input range of the A/D as 0 to 4.096 volts. With this option, the DAC must be configured to generate its own reference voltage (using the INT_1V_DAC12 or INT_2V_DAC12 options with the Init_Analog_IO function).

5.0 Volt Reference Jumper

The 5.0 Reference Jumper, labeled J5, and named "5V Ref" on the silkscreen of the Analog I/O Wildcard, connects the onboard 5 volt analog supply to the reference input pin on the A/D. This configures the input range of the A/D as 0 to 5.0 volts. With this option, the DAC must be configured to generate its own reference voltage (using the INT_1V_DAC12 or INT_2V_DAC12 options with the Init_Analog_IO function).

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