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PC/104 Module Supports Low-Noise Embedded Data-Acq

The manufacturer says . . .

ChipCenter's Alex Mendelsohn says . . .

True 16-Bit PC/104 Analog I/O Module Has Filters, IRQs, Digital I/O, DMA, Ext Temp, and Autoscan Mode The MPC560 from Micro/sys is an extremely capable data-acquisition subsystem for embedded systems. The PC/104 module includes 32 channels of 16-bit A/D input, and 4 channels of 14-bit D/A output. Significant design attention was given to maintaining a low-noise analog subsystem that could deliver true 16-bit and 14-bit performance. The rigorous analog input subsystem includes programmable gain amplifiers, programmable low-pass filters, a 16-channel differential-input mode (DI), and input overvoltage protection to ± 40 V, with power on or off. The analog-output subsystem includes one-pole low-pass filters and output buffers capable of driving cables and other highly capacitive loads. An onboard EEPROM holds calibration data that can be used for installed, end-to-end calibration of input channels. The Autoscan mode of the analog input section adds a wealth of choices to the system designer. Various onboard or external "pacer clocks" can be used to cause periodic conversions to occur without any software intervention. An SRAM-based storage area is used to set the include/exclude control, mode (SE or DI), gain, and low-pass filter knee for each channel individually. Once initiated, the Autoscan mode proceeds, using DMA for transferring conversion results into system RAM. A terminal count interrupt notifies the program when the DMA buffers have been filled. The MPC560 also includes 12 general-purpose digital I/O lines. These flexible I/O lines can be set individually as input, output, or inputs that generate an IRQ when they transition from low to high. Fault protection is provided on all 12 digital I/O lines. The analog-input range is ± 10.1 V or ± 5.05 V. The analog-output range is ± 10.1 V, and all outputs are set to 0 V upon power-up or reset. Input and output accuracy is 0.02 percent of full scale across the operating-temperature range. The input circuitry will allow sampling of 20 V p-p at 35 kHz, or 5 V p-p at 100 kHz. The output circuitry can generate 20 V p-p signals at 15 kHz. Sample programs and full documentation are provided with the board. An industrial-temperature version, the MPC560-ET, is also available. The MPC560-ET has guaranteed accuracy from -40°C to +85°C. Both versions of the MPC560 require only a single 5 V supply to operate. Line regulation on the 5 V input is 0.001 percent of full scale. The basic commercial-temperature 16-input MPC560 is $425 in single quantity. The 4-channel analog output option is $105, and an additional 16 inputs are $20. Substantial quantity discounts are available. Contact Technical Sales Dept. Micro/sys, Inc. 3730 Park Place Montrose, CA 91020 Phone: (818) 244-4600 FAX: (818) 244-4246 E-mail: info@embeddedsys.com Web: www.embeddedsys.com

Micro/sys is one of those companies that's been around quite a while (since 1976), but doesn't often take top-headline billing. Nonetheless, the firm is known for its PC/104 modules such as this Model MPC560, as well as quite a few products for PC/104-Plus, VMEbus, EBX, and the STD Bus, to name a few. Micro/sys also makes a line of proprietary data-acq products and embedded processor boards, too. For data acquisition and control, as well as compact instrumentation and systems, PC/104 lets you mix-and-match modules from disparate vendors. Indeed, PC/104's modularity is what lets you create arrays of functions and capabilities to suit application-specific needs. In general, you can choose from PC/104 single-board computers, DSP modules, display cards, Ethernet controllers, and I/O modules of virtually every description from many PC/104 vendors. Stackability PC/104's physical format of 3.6" × 3.8" is almost always considered for its stackability and the fact that a system doesn't need a backplane per se. However, it's not always necessary to stack PC/104 modules to achieve satisfactory high-density packaging. They can be used in nonstacked arrays, where you benefit purely from their mix-and-match modularity. Although the company's press statement mentions variations of the MPC560 for different temperature ranges, it's worth noting that the MPC560 is appropriate for applications where environmental hardening and ESD protection are also paramount. More on that in a moment. Configurability For the MPC560, its flexibility as a module is enhanced by its configurability. For example, its 32-channel multiplexed input supports individual channel selection. That means that you can select either a single-ended or a differential configuration for any analog input—in any combination. As alluded to in the press release, the analog inputs can also be operated in what Micro/sys calls Basic or Autoscan modes. In Basic mode you get direct control of settings for input amplifier gain, channel MUXing, and filtering. A default Basic mode from reset permits readings of individual channels from software with polled/IRQ. Alternatively, you can choose the system's Autoscan mode. In Autoscan you can preset individual channel attributes, and then set a scan rate and wait for an external trigger. Autoscan waits for the trigger, or software, to start the system's so-called pacer clock. It then runs through each channel with preset values, storing data into host-processor memory using DMA. The board supports DMA modes 5, 6, and 7. Interrupt transfers support IRQs 3, 4, 5, 6, 7, 9, 10, 11, 12, 14, and 15. The company's press release nicely summarizes the various I/O options and ranges, but doesn't mention that the output D/A converter section includes niceties such as a Faraday shield, as well as the built-in filtering. Again, it's features such as these that make this board suitable for industrial environments where spikes and noise are factors that must be contended with often. The press statement mentions the MPC560's analog-output subsystem with one-pole low-pass filter and high-drive output buffers. What it doesn't say is that the buffer also helps stop noise on system cables from coming back onto the die of the system's D/A converter. This product is billed by Micro/sys as an ultra low-noise design, so any steps that can be taken to preclude noise have been taken. These steps include conditioning the system's analog power. Although derived from the PC/104 bus's 5 V lines, the MPC5560 includes extra LC-type I/O filters, as well as post-regulators following the onboard DC-to-DC converters. This combo ensures closely controlled line and load regulation, helping to thwart noise, and maintain calibration as well. Although the board's on-card DC-to-DC converters provide the positive and negative voltages for the MPC560's analog front-end circuits, these voltages aren't good enough for an instrumentation-grade design such as this. To ensure better line and load regulation, the product's DC-to-DC converters are followed with LDO (low-dropout) regulators. The LDOs also cut low-frequency noise. The Golf Gambit Micro/sys states that designing a data-acq system is akin to learning to play golf. Anyone can hit the ball, but then you can spend the rest of your life refining the game. Similarly, anyone can design a system with an A/D converter and take a sample, but then you can spend a lot of engineering time and talent refining it to achieve performance levels equivalent to what you can buy off-the-shelf. This analogy is especially applicable to high-performance instruments. For these reasons, Micro/sys advocates buying PC/104 boards such as the less-than-$500 Model MPC560. You'll benefit from a proven design that accounts for accuracy issues, drift, noise, and temperature. It will have an AC response to full-power bandwidth and a defined slew rate. Indeed, the MPC560 is a set-and-forget drop-in PC/104 product that can enhance an embedded data-acq system based on it. Lastly, Micro/sys supports this product with software, and offers system-level bits for real-time operating systems, as well as MS-DOS, Linux, Windows CE, Windows NT, and other Microsoft Windows wares. Since its inception back in 1976, the company has also embraced open-system standards, which is in lockstep with the open PC/104 standard, and the company has also played a role on the boards of a number of embedded-industry trade associations. You'll be in good PC/104 company with Micro/sys. Give 'em a call.

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