The Lab-PC+ is a low-cost, multifunction analog, digital, and timing I/O board for ISA computers. It has a 12-bit ADC with eight analog inputs, configurable as eight single-ended or four differential inputs, two 12-bit DACs with voltage outputs, 24 lines of TTL-compatible digital input and output, and three user-available 16-bit counter/timer channels for timing input and output. The PC bus interface has 8-bit data paths with circuitry for interrupts and DMA.

For additional analog inputs and signal conditioning, you can use the SCXI signal conditioning system to multiplex, isolate, and amplify up to 384 low-level signals into a single board.

The Lab-PC+ is ideal for laboratory work in industrial and academic environments. The multichannel analog input is useful in signal analysis, data logging, temperature measurement, and DC voltage measurement. The analog output channels can generate experimental stimuli, machine and process control signals, and analog functions. You can use the 24 TTL-compatible digital I/O lines for switching external devices such as transistors and solid-state relays, for reading the status of external digital logic, and for generating interrupts. You can use the three counter/timers to synchronize events, generate pulses, and measure frequency and time. The PC equipped with the Lab-PC+ is a versatile, cost-effective platform for laboratory test, measurement, and control.

Figure 1 shows the block diagram of the Lab-PC+ circuitry. The following paragraphs describe the major functions of the hardware.

The Lab-PC+ has two CMOS analog input multiplexers connected to eight analog input channels. The input circuitry gives input overvoltage protection of ±45 V powered on or powered off. You can use the analog input channels as eight single-ended inputs, eight pseudodifferential inputs with a shared common, or four fully differential inputs.

Voltage input range is jumper configurable for 0 to 10 V (unipolar) or ±5 V (bipolar). A software-programmable gain amplifier has gain selections of 1, 2, 5, 10, 20, 50, or 100. The Lab-PC+ has a 12-bit ADC with analog signal resolution of 2.44 mV at a gain of 1. You can achieve Þner resolutions down to 24.4 µV by using a higher gain. The 12-bit output of the ADC is automatically sign-extended to 16 bits.

The Lab-PC+ performs both single A/D conversions and multiple A/D conversions of a set number of samples. A 512-word-deep FIFO memory buffers the data during multiple A/D conversions. Multiple A/D conversions can be handled by programmed I/O, interrupts, or DMA.

An onboard counter/timer controls the timing of multiple A/D conversions. The counter/timer generates the sample interval clock with a resolution of 1 µs. As an alternative, an external signal can generate the timing for the sample interval. Data acquisition with the Lab-PC+ is available in three modes: 1) continuous acquisition of a single channel, 2) multichannel acquisition with continuous scanning, or 3) multichannel acquisition with interval scanning. In the third mode, all channels are scanned at one sample interval, with a second interval determining the time before repeating the scan. Both single A/D conversions and multiple A/D conversion sample sequences are initiated from either software or external timing control signals.

There are two hardware triggering modes - pretrigger mode and posttrigger mode. In pretrigger mode, a programmed number of samples are acquired before a trigger is received at the external trigger input. In posttrigger mode, a programmed number of samples are acquired either immediately, or when a trigger is received at the external trigger input. By combining the pretrigger and posttrigger modes, the Lab-PC+ can acquire data before and after a trigger condition.

Any number of channels between 2 and 8, in single-ended, or between 1 and 4 in differential mode, can be scanned in the multichannel acquisition mode. These channels are scanned in a round-robin sequence, taking one reading per interval, with scanning always occurring in the same order, from the number of channels selected to channel 0.

The Lab-PC+ generates both interrupts and DMA requests on the ISA I/O channel. You can generate interrupts whenever an A/D measurement is available from the ADC FIFO, upon error conditions, when the DMA process has reached terminal count, upon receiving digital I/O handshaking signals, or when one of the onboard timer clocks generates a pulse. You can generate DMA requests whenever an A/D measurement is available from the ADC FIFO.

The Lab-PC+ has two double-buffered 12-bit DACs that are connected to two analog output channels. You can configure each channel independently for unipolar (0 to 10 V) or jumper-selectable, bipolar (±5 V) operation. The resolution of the 12-bit DAC is 2.44 mV in both polarities.

You can handle waveform generation by programming I/O or interrupts. One of the 8253 counter/timers is used with the DACs for waveform generation. The counter/timer generates periodic interrupts and update signals for the double-buffered DACs.

The Lab-PC+ has 24 digital I/O lines, configurable as three 8-bit ports for input, output, bidirectional, or handshaking modes. Two of the ports can drive Darlington transistors directly for higher-current applications. The digital I/O lines are TTL compatible. The digital output port can sink 1.7 mA on each line.

The following software is included with the Lab-PC+: * NI-DAQ for Windows 95/NT/3.1/3.1J * DAQWare

Detailed information on NI-DAQ can be found on page 2-98.

The following software is available separately: * LabVIEW * LabWindows/CVI * LabWindows * Measure * VirtualBench * ComponentWorks * NI-DAQ for DOS and DOS/V Detailed information on this software can be found in Section 2.

Lab-PC+ and software 776703-01 50-pin Connector Blocks and Cables CB-50LP low-cost connector block 777101-01 Type NB1 50-pin to 50-pin ribbon cable 0.5 m 180524-05 1 m 180524-10 2 m 180524-20

For more accessory options, refer to the Related Products list.

© 1996, National Instruments All Rights Reserved

Product and company names listed are trademarks or trade names of their respective companies.

Instrupedia, 1996