Laboratory Interfacing Handbook

This document is the "LABORATORY INTERFACING HANDBOOK" by Digital Equipment Corporation, published in December 1986.

The handbook serves as a comprehensive guide for scientists and programmers on the practical aspects of interfacing computers to laboratory devices for "realtime" applications. It targets a range of users from novices seeking to understand "turnkey" systems in depth, to beginning programmers wanting to modify software or start their own, and advanced programmers new to realtime development. The emphasis is on problem-solving and the intelligent application of these systems.

Key areas covered in detail include:

1. Introduction to Realtime Computing: Defines realtime operations (data acquisition and control), and the three main forms of realtime data: analog signals, discrete digital signals, and time-interval measurements. It also introduces "intelligent instruments" with built-in microprocessors and the need for communication links.

2. Realtime I/O Modules: Explains the fundamental components and functions of I/O modules, including their role in data translation, signal conditioning, buffering, and flow control (device/module synchronization via triggering and handshaking, and module/system synchronization via Programmed I/O (PIO) and Direct Memory Access (DMA)). It also details hardware configuration (jumpers, DIP-switches) and various programming approaches (direct device control, device drivers, subroutine libraries, user-friendly interfaces).

3. Analog Input and Output: Provides in-depth guidance on handling analog signals, covering digital representation of signal amplitude and time, different connection schemes (single-ended, pseudo-differential, differential), methods to control noise (common-mode, electrostatic, magnetic, crosstalk, multiplexer, residual, signal averaging), selection of gain factors (fixed, programmable, autoranging), sampling rates (time-domain and frequency-domain analyses, aliasing), and trigger modes. Analog output concepts are also discussed.

4. Digital I/O: Explains how to perform digital input/output, including properties of TTL circuits, generating TTL levels from switch closures, connecting devices (cable types, controlling crosstalk and ringing), and distinguishing between discrete and parallel digital I/O, along with their respective triggering methods.

5. Instrument Bus Communication: Dedicated chapters detail the use of the IEEE 488 Instrument Bus (GPIB), covering roles (talker, listener, controller), instrument addressing, message communication, status testing (serial and parallel polls, service requests), and managing remote/local states.

6. Serial Device Control: Explains serial data communication (bit-by-bit transfer) and how to configure devices for RS-232 compatibility, including selecting baud rate, start/stop bits, data bits, parity, and handshaking methods (hardware, software, ACK/NAK protocol). It also covers physical connection types and cable length considerations.

7. Clock/Counter Modules: Describes the internal operation and various modes of clock/counter modules for measuring time intervals and counting pulses.

8. Advanced Realtime Programming Techniques: Discusses sophisticated programming methods such as buffer management (ring buffers, double/multi-buffering), direct device control on virtual systems (accessing device registers, processor priority levels), and interrupt programming on virtual, multi-tasking systems.

9. Realtime System Performance: Analyzes factors affecting system throughput and response time, including system bus structure and bandwidth, CPU design and speed, operating system characteristics (task scheduling, I/O programming services, intertask synchronization), and I/O controller speed and features (DMA vs. PIO, special functions, buffer memory).

The handbook, featuring Digital's VAX and PDP-11 systems, aims to equip users with the knowledge to select appropriate hardware and software, and optimize performance for their laboratory data acquisition and control applications.