12-Bit Analog Output Cards
PCI-DA12-8 and PCI-DA12-16 are full-size cards that can be installed in long slots of PCI-Bus computers. They contain eight and sixteen independent double-buffered, digital-to-analog converters (DACs), and three 16-bit counter/timers. The PCI-DA12-2, -4, and -6 have two, four, and six DACs respectively. All of these cards have 8255 Compatible digital input/outputs, 16bits are available on the PCI-DA12-2/4/6 models, and all 24 bits are available on the PCI-DA12-8/16 models. On the latter card a cable and bracket is provided to bring the 40-pin header signals to a 37-pin DB connector on an adjacent mounting bracket.
The DACs are double-buffered and can be updated individually or simultaneously. To assure that there will not be excessive outputs to external circuits when the card is plugged in, automatic circuits limit analog outputs to 15 percent of full scale when the card is powered up. Upon power-up, the DAC reference voltage is set to that low voltage and the card is set in the Simultaneous Update mode. Then, after values are loaded into the DACs, you can use a software command to switch the DACs to their respective full scale ranges.
Analog output ranges available are:
- 0 to +2.5V
- 0 to +5V
- 0 to +10V
- -2.5 to +2.5V
- -5 to +5V
- -10V to +10V
- 4 mA to 20 mA
Higher drive current available on request
Calibration constants are generated and stored in software using a program included with the cards. ZERO (or OFFSET) constants are stored in EEPROM along with SPAN calibration constants. Further, the EEPROM stores a table of ranges that are assigned to each channel.
On the PCI-DA12-8 and PCI-DA12-16, a type 8255 Programmable Peripheral (PPI) IC provides 24 bits of digital input/output. The PPI is operated in Mode 0 and provides three 8-bit ports (A, B, and C). Each port can be individually programmed for input or output. Port C can be further configured as two 4-bit ports. Each digital I/O line is buffered by a type LS245 tristate transceiver that can source 15 mA and sink 24 mA (64 mA on request as a factory-installed option). Pull-ups on the card assure that there are no erroneous outputs at power-up and the buffers are configured for input or output use by direction assignment from a control register in the PPI.
The PCI-DA12-2/4/6 cards use the same 8255 PPI, but bring only ports A and B to the connector, providing 16-bits of DI/O
Three 16-bit down counters, in a type 8254 IC, are included on the PCI-DA12-8 and PCI-DA12-16. These are configured as Event counters (See Block Diagram) and can also be used as a frequency source derived from an on-board 1 MHz crystal-controlled oscillator. These counters can generate IRQs at a programmed frequency, and/or initiate DAC updates. This allows for very precise timing of waveform generation.
I/O connections for the DACs are made at a 37-pin Sub-D Male connector on the card mounting bracket. On the PCI-DA12-8/16 I/O connections for the digital inputs/outputs and the counter/timers are made through a 40-pin insulation displacement header and ribbon cable to a second bracket that can install alongside the first. The PCI-DA12-2/4/6 models bring 16-bits of Digital I/O to the same 37-pin connector as the DAC data.