Use of CAMAC for computer interface

Mini- and micro-computers have now become an indispensable part of many NMR spectrometers. A major reason for this, of course, is the ever decreasing cost per performance of the entire computer family. In fact, the hardware cost of the computer itself is now so low that a major cost, either in terms of actual outlay or of time and effort, is that 

There are several reasons why a researcher may choose to develop his own interfaces and software. An obvious one is to reduce the initial outlay of money and develop the necessary software and interface as an educational experience. Another is to develop a system more suited to the particular experimental needs than to buy a system which lacks the necessary versatility or which has highly developed features which are not needed. 

This section points out the existence, apparently not well known in NMR circles, of a middle ground between developing a computer interface from scratch and buying a data system already interfaced to the spectrometer. We have assembled such an interface using CAMAC modules which are extensively used in particle physics experiments and we give a brief description here as an example of what is possible (Fukushima and Swenson, 1980). 

The hardware cost associated with CAMAC also represents a middle ground between a homebuilt interface and a commercially built interface. The software must still be written for the particular system as in the case of a homebuilt interface but, due to the standardization of the commands required for the modules, the task is a little easier with the CAMAC interface. Furthermore, since CAMAC modules are commercially available, any programs written for a CAMAC system can be adapted quite easily for another CAMAC system. 

CAMAC is an international standard for modular computer instrumentation. It specifies the electrical, mechanical, and functional characteristics of modular instruments to be plugged into a standard multi-receptacle crate which, in turn, can be interfaced to a minicomputer. The unique feature of CAMAC systems, as opposed to other modular systems, is that the modules not only get power from the crate but the data-way between the modules and the crate controller can carry 24-bits of data in each direction in addition to various function, address, and flag signals. The controller resides in the crate as a module and acts as an interface between the modules and a specific computer. Some of the lines in the dataway are location-specific so that a module in a given slot can be addressed by the controller. The modules (except for the controller) cannot communicate with other modules except through the controller. 

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