Microprocessor Interface Circuits

The major 8-bit, 16-bit and 32-bit microprocessors have dif- ferent control signal timing. There are also a number of speed options. The DP8400 family was designed, not for a specific microprocessor, but rather, significant control flexi- bility has been provided on both the DP84XX DRAM control- ler/drivers and the DP84XX error correction devices for easy interface to any microprocessor. However, a certain amount of ‘‘glue’’ is necessary to interface to these LSI cir- cuits, usually in the form of a number of MSI/SSI logic cir- cuits. Not only can this be costly in board space utilization, but it is usually the one place where the most design related problems occur in system development.

Figures 13 and 14 show the DP8400 family solution to this problem—the DP84XX2 series of microprocessor interface circuits. Figure 13 shows how the DP84300 refresh timer and the DP84XX2 microprocessor interface circuit connect to the DP8409A and various microprocessors for a typical application. Figure 14 shows the DP8409A and the DP8400 together in a microprocessor-based memory system using DRAMs, with double bit error detect and single bit error cor- rect capability. In addition, it shows that with the simple ad- dition of some standard data buffers, how the system can implement byte writing to the DRAM array.

This system structure requires the insertion of few or no wait states during a memory access cycle, thus maximizing throughput. The DP84XX2 circuits have been designed to work with all of National’s DRAM controller/drivers to con- trol refreshing so that system throughput is affected only when absolutely necessary. First, in any refresh clock peri- od of 16 ms, hidden refreshing is given maximum opportuni- ty. This can be helped with the optional DP84300 refresh interval generator which offers maximum high-to-low ratio- ing of RFCK. Second, when a hidden refresh does not occur in a particular RFCK cycle, a forced refresh may still not affect a slow access cycle. The worst-case is when an ac- cess is pending during a forced refresh, in which case a three wait state delay is usually the maximum penalty.

Usually two DP84XX2 type chips would be required to inter- face between any microprocessor and the DP8400/ DP8409A combined system. These chips would handle the read/write control as well as error detection and correction control. Table VII shows the individual DP84XX2 circuits that would be used in systems with no error correction, thus requiring only the DP84XX DRAM controller/driver function.

†The select wait input to the DP843X2 chip inserts a wait state during accessing. This is necessary for very fast micro- processors.

TL/F/5012 – 17

FIGURE 13. Connecting the DP8409A between 16-Bit Microprocessor and Memory

DP8400 specifications

The National Instruments DP8400 is a robust and versatile data acquisition and control platform that stands out in the landscape of advanced instrumentation solutions. Designed to meet the demands of both academic and industrial applications, the DP8400 serves as a comprehensive tool for engineers and researchers alike, facilitating data collection, processing, and analysis in real-time.

One of the key features of the DP8400 is its high-performance data acquisition capability. It supports a wide range of input types, including analog, digital, and thermocouples, allowing users to connect various sensors and devices easily. With sampling rates of up to 1 MHz and resolutions of up to 24 bits, this instrument ensures precise and reliable data capture across diverse applications.

The DP8400 also integrates advanced signal processing technologies, including built-in filtering, signal conditioning, and data preprocessing capabilities. These features enable users to refine their measurements and extract meaningful insights from raw data, reducing the need for extensive post-processing. This is particularly beneficial in complex experiments where signal noise can interfere with results.

Another notable characteristic of the DP8400 is its versatile connectivity options. Users can connect to the device using USB, Ethernet, or wireless interfaces, facilitating seamless integration into existing laboratory setups or remote monitoring configurations. The device is compatible with various software platforms, including LabVIEW and MATLAB, providing users with familiar environments for programming and data visualization.

The DP8400 also boasts robust data storage capabilities, allowing for high-speed data logging and management. With onboard memory and support for external storage devices, users can capture extensive datasets without loss of performance. This is especially useful in long-duration experiments or when conducting time-series analysis.

In terms of durability, the DP8400 is built to withstand challenging environments, featuring rugged housing and protection against dust and moisture. This makes it suitable for both laboratory and field applications, providing reliability in diverse operating conditions.

Overall, the National Instruments DP8400 represents a powerful solution for data acquisition and analysis, combining high performance, advanced features, and exceptional flexibility. Whether for educational purposes, research projects, or industrial applications, the DP8400 is an essential tool for engineers and scientists looking to streamline their data collection and enhance their analytical capabilities. With its user-friendly interface and extensive support, it empowers users to explore new frontiers in measurement science.