2.2Digital to Analog Converters
The digital to analog (D/A) section of the DAQ-16 consists of two independent 12-bit multiplying D/A converters, and two independent two-stage output amplifiers. Digital data, (output to the D/A converter by the CPU), is converted to an analog voltage by the D/A converter, amplified by the output amplifiers and becomes output to the 62 pin connector at CN1. The D/A converters used on the DAQ-16 are 12-bit resolution converters. Of the 16 bits written to the D/A, only the 12 least significant bits (D0 - D11) are used for the conversion. The 4 most significant bits (D12 - D15) are ignored.
The DAQ-16 implements multiplying D/A converters which makes the analog output proportional to a reference voltage applied to the D/A. Under normal circumstances, the reference voltage should be applied from the internal +5V reference source. An external reference voltage may also be supplied to the D/A. This input from the D-62 connector should not exceed 5 volts and has a typical input impedance of 7.5Kohms. The D/A reference voltage source is selected using jumper J3 as illustrated in Figure 2-4.
D/A channel 0 reference
Internal Source 
4 5 6
J3
1 2 3
Internal Source | External Source |
D/A channel 1 reference
Figure 2-4. Jumper J3 Configuration
The D/A converter channels may also be operated in unipolar mode: 0 to +5 volts, or bipolar
mode: -5 to +5 volts. The output mode is selected using jumper J4 as shown in Figure 2-5. In addition, a gain selection jumper is provided to select an output gain of 1 or 2. When using an external voltage reference, this gain can be used to amplify the D/A output for small reference voltages.
WARNING: When the internal voltage reference is used, the D/A gain MUST be set to the
gain = 1 position.
