| Voltage | | Unipolar | | | Bipolar | | |
| | | | | |
| | | Code | | | Code | | |
| -5 | | n/a | | 1111 1000 0000 0000 | |
| -2.5 | | n/a | | 1111 1100 0000 0000 | |
| 0 | 0000 | 0000 | 0000 | 0000 | 0000 | 0000 | 0000 | 0000 | |
| 2.5 | 0000 | 0100 | 0000 | 0000 | 0000 | 0100 | 0000 | 0000 | |
| 5 | 0000 | 1000 | 0000 | 0000 | 0000 | 0111 | 1111 | 1111 | |
| 10 | 0000 1111 1111 1111 | | n/a | | |
| | | | | | | | | | |
Table 2-2. A/D Conversion Format Examples
NOTE: The 'voltage' column is the voltage applied to the A/D converter. This voltage is equivalent to the input voltage multiplied by the amplifier gain.
2.2Digital to Analog Converters
The digital to analog (D/A) section of the DAQ-12 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-12 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-12 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 J4 as illustrated in Figure 2-4.
D/A channel 0 reference
Internal Source 
External Source
4 5 6
J4
1 2 3
Internal Source | External Source |
D/A channel 1 reference
Figure 2-4. Jumper J4 Configuration
