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Scientific Solutions ^® Inc.

MCDAS ^TM 1612/16 MicroChannel Products

Product Description Our Solution Includes Key Features Applications Functional Description Analog-to-Digital Conversion Digital-to-Analog Conversion Timer/Counter Digital I/O Interrupts Technical Specifications Software Application Assistance & Reliability

The MC-DAS series of data acquisition products turn PS/2 Micro Channel computers into a powerful educational, industrial or scientific workstation. Key data acquisition & control functions are included in one high performance, low cost package including: Self calibrating 12 or 16 bit ADC, software programmable gain amplifiers, five high speed 16 bit timer/counters, digital I/O and analog-to-digital conversion.

Product Description

Turn your IBM PS/2 MicroChannel or compatible computer into a powerful educational, industrial, or scientific workstation. Key data acquisition & control functions are included in one high performance, low cost package. The self-calibrating, 12-bit analog to digital converter (ADC) handles 16 single-ended or 8 differential input channels at rates up to 100,000 samples/second. Using the Programmable Option Select (POS) technology of the MicroChannel, all analog input features are software configurable.

The precision gain amplifier (software programmable gains of 1, 2, 10, and 100) provides input resolutions between ±100 mV and ±10 Volts. One 12-bit digital to analog converter (DAC) supplies 5mA (2K Ohm load) across either a ±10 Volt or 0 to +10 Volt output range. Five 16-bit precision timer/counters can time intervals to one microsecond or count events to 160 nanosecond resolution. Digital input and output lines (two each) provide access to external devices. A 37-pin D-shell connector interfaces all features to external devices. Completing the system are a 40-pin screw terminal board with RF-shielded cable, the LabPac software package, and utility software.

Our Solution Includes

• An advanced Data Acquisition & Control interface for the PS/2 MicroChannel
• LabPac - flexible, universal driver for all MS DOS languages
• Data streaming software
• Utility software
• A 5-ft. RF-shielded cable
• A 40-pin Screw Terminal Board
• A complete Handbook

Key Features

• Complete MicroChannel POS register support
• All A/D features are software configurable
• Self-calibrating, 12-bit ADC 1612 (MC-DAS 1612) or 16 bit ADC (MC-DAS 1616)
• A/D sampling rates to 100,000/second
• 16 single-ended/ 8 differential analog inputs
• Software programmable gain (1, 2, 10, 100)
• Accurate, timed A/D - use with channel auto-scan for Burst Mode performance
• 16 sample FIFO for continuous ADC data
• DMA transfer of ADC data (MicroChannel bus arbitration & Burst Mode support)
• Five high speed 16-bit timer/counters
• One 12-bit D/A converter (2 voltage ranges)
• Two lines each of digital in/digital out
• Hardware interrupts from multiple sources

Applications

• BioMedical (EEG, stress testing, cellular stimulation)
• Energy Management (temperature control, pressure sensing)
• Chromatography
• Education (Physical Science Labs, student projects)
• Psychology (polygraph, stimulus control, interval timing)
• Process Automation (production line control, product counting)
• Test and Measurement (Particle counter, metal fatigue detection)

Functional Description

The MC-DAS installs internally into an expansion slot of an IBM PS/2 series, MicroChannel computer or compatible. Complete cabling and a screw terminal board are provided for easy access to all input and output lines. The MC-DAS fully conforms to the MicroChannel bus specification as an I/O slave, DMA capable. POS register implementation allows the selection of one of seven I/O base locations and four interrupt levels.

Analog-to-Digital Conversion (ADC)

Designed for maximum flexibility, all features of the analog to digital converter are software configurable. There are no jumpers or switches to change when resetting the MC-DAS for different input conditions. The analog to digital converter (ADC) is a 12-bit or 16 bit successive approximation converter with a 7.5 microsecond conversion time. The software configurable features of the converter are: Input Type (single-ended or differential), Input Range (unipolar or bipolar), Channel Select (single or autoscan), Programmable Gain (1, 2, 10, or 100), ADC trigger, ADC trigger timing, Direct Memory Access (DMA) conditions (arbitration level and type, Burst Mode, and non-DMA), and Re-calibration.

The MC-DAS is software configured for 16 single-ended or 8 true differential input lines. All analog input lines have a 100M Ohm input impedance and are multiplexed to the ADC. A programmable, precision gain amplifier (1, 2, 10, or 100) at the input to the Sample & Hold circuit allows the input range to vary from ±100mV to ±10V. The gain of 100 can be modified by a precision resistor for gains up to 1000. Examples of sensor types that can be used as analog inputs are: Temperature, Flow, Displacement, Voltage, Current, Acceleration, Velocity, Level, Pressure, Moisture, and Humidity.

A conversion is started by a software command, a trigger signal from a pacer clock, a rising edge from an external source, or self-triggered by the end of the last conversion. Channels can be selected for conversion one at a time or as a set of consecutive inputs. Software enabled, the auto-scan feature automatically increments the channel number with each conversion. Both the starting and ending channel in the sequence are software selectable.

The self-calibration feature of the ADC allows the nulling of internal conversion errors by resetting the ADC characteristics for the current input conditions using a software command. Conversion errors due to differential non-linearity or temperature drift are effectively eliminated because the ADC will be calibrated for the current environmental state. When going from low to high gains, the only required hardware adjustment is for the input offset. In many cases this input offset can be predetermined and subtracted out in software, freeing the user of all adjustments.

Converted data is transferred to an on-board, 16 sample FIFO buffer. High speed transfer of the sampled data to a memory buffer is possible using the Direct Memory Access (DMA) capabilities of the MicroChannel. DMA arbitration levels, immediate rearbitration, and burst mode transfers are fully supported. When DMA is used, the end of the conversion strobe will initiate the DMA request. When not using DMA, the end of a conversion can be detected using an interrupt or by polling the status register. Data is transferred at the end of a conversion by reading the converted data byte from the FIFO buffer or via DMA transfer.

Functional Description - Standard ADC Features

• All ADC features are set by software
• 12 bit resolution (4096 equal intervals) or 16 bit resolution (65535 equal intervals)
• 100,000/second maximum sampling rate
• 16 Single-ended or 8 Differential input channels
• Selectable input range
  0 to +10 Volt (unipolar, 2.44mV / interval)
  ±10 Volt (bipolar, 4.88mV / interval)
• DMA transfer of samples to memory
  Supports all Micro-Channel bus arbitration levels
  Supports Burst Mode transfers
• Choice of A/D trigger (software controlled)
  Timed intervals using gated pacer clock
  Maximum rate channel scans at timed intervals
  External TTL pulse (rising edge)
  Software initiated strobe
• Sampling Modes
  Single channel up to 100,000/second
  Non-consecutive channels up to 50,000/second
  Auto-scan blocks of channels up to 100,000/second
  Maximum rate channel bursts at timed intervals
• Data latched in 16 sample FIFO buffer
• Self-calibrating ADC
• Hardware interrupts (software controlled) on:
  • End of Conversion
  • A/D Data Overrun
  • DMA Terminal Count
• Software programmable gains of 1, 2, 10, or 100

Digital-to-Analog Conversion (DAC)

The 12-bit digital to analog converter (DAC) has jumper selectable output ranges of ±10 Volts and 0 to +10 Volts. Each output value is latched and remains constant until the next digital value is presented to the DAC. An output buffer generates 5mA of current across the voltage range and permits connection to 2000 Ohm loads. Programming involves writing a 12-bit value to one I/O location.

Functional Description - Standard DAC Features

• 12 bit resolution (4096 equal intervals)
• Ten microsecond settling time
• 100 KHz maximum output rate (software controlled)
• Two jumper selectable output ranges 0 to +10 Volts
• 5mA output current
• Buffered output
  

System Timer/Counter (STC)

Five independent 16-bit timer/counters count TTL compatible pulses (rising or falling edge) generated from a wide range of equipment and sensors. Six separate source and gate input lines are provided on the external connector for signals that can be used by any counter. A TTL compatible pulse/level output signal (1 TTL load) is available from three counters.

Each gateable counter can count up or down (binary or binary coded decimal format) while the accumulated count may be read at any time without disturbing the counting process. Each of the counters can be connected to others to form a counter with resolution up to 80 bits. The counters can be driven by an on-board 1MHz crystal giving them resolutions from 1 microsecond to 10 milliseconds. External events can be counted at speeds to 6.25 MHz. Programming is accomplished through an 8-bit command register, an 8-bit status register, and a 16-bit data port. Instructions for direct programming are contained in the Handbook

Functional Description - Standard Timer/Counter Features

• Five independent 16-bit counters
• Five on-board sources for interval timing to one microsecond resolution (1MHz oscillator)
• Event counting to 6.25MHz (160 nanosec. intervals)
• 10 external I/O connections
  • 4 outputs (1 TTL load - pulse or level)
  • 3 source inputs (TTL compatible pulses)
  • 3 gate inputs (TTL edge or level, control counting or serve as input signal)
• Counter outputs can:
  • Trigger A/D conversions
  • Trigger hardware interrupts
  • Send square and complex waveforms
  • Gate counters
  • Drive TTL devices

Digital Input/Output (DIO)

The MC-DAS contains four lines of digital I/O. Two lines are set as inputs and two lines are set as outputs (supply 24mA). The input lines are monitored by reading the value in the MC-DAS Status Register and decoding two bits. The output lines are changed by setting/clearing two bits in a command word and writing the value to the MC-DAS Control Register.

Interrupts

Hardware interrupts allow the computer's processor to react to special events when they occur. Level sensitive interrupts and interrupt sharing are implemented as required by the MicroChannel bus hardware specification. The MC-DAS provides four software enabled sources for hardware interrupts. The sources are timer/counter output, end of A/D conversion, A/D data overrun, and DMA transfer completed. External signals can be used through the counter source inputs. Software allows any of the interrupt sources on the board to be connected to any of four hardware interrupt request lines (IRQ3, 5, 11, 15). Hardware interrupts require special software called Interrupt Service Routines to process the interrupt.

Technical Specifications

System Accuracy

The analog to digital conversion system of the MC-DAS 1612 consists of the analog input multiplexers, the precision gain amplifier, the sample & hold, and the ADC. Each of the parts of the system have individual accuracy specs. System accuracy, however, is the precision of the signal when it is processed through all of the parts. An accuracy spec can only be determined by testing complete systems. Comprehensive tests of the MC-DAS 1612 indicate its system accuracy is 12 bits ±1/10 LSB. This means the full 12-bit resolution of the ADC is accurately delivered.

Tests of the MC-DAS 1616 indicate its system accuracy is 14 bits. For any 100 samples, 70% will be accurate to 16 bits, with the remaining samples falling within a normal distribution around the correct value. The main factor decreasing the system accuracy is wideband noise inside the ADC. Noise in the digital domain can be reduced by sampling at higher rates and averaging multiple samples. Over sampling spreads the ADC noise over a wider band. Averaging applies a low-pass response which filters noise above the desired signal bandwidth. Depending on the waveform under analysis, there are different digital low-pass filters that can be applied. All major statistical and analytical packages contain filter algorithms to apply to raw data.