Chapter 38 The RW-400-a new polymorphic data system 481

Multiply Accumulate wherein the contents of H are multiplied by C and added to A; and Transmit where the contents of C are stored in H.

The ten program control instructions are Store, Store Double Length Accumulator, Load Accumulator, Insert Mask in the S Register, Stop, Link Jump, Compare Jump, Tally Jump, Test Jump and a Multi-purpose Shift.

The five external instructions are those which cause data to be transmitted to or received from a device external to the computer. Each command is multi-purpose in nature and hence equivalent to several conventional external instructions. The commands are-Command Output, Data Input, Conditional Data Input, Data Output and Character Transfer. A comprehensive discussion of the variation of each of these commands is not pertinent to this article. Suffice it to say that commands are available for carrying out a wide variety of intermodule data communication.

The interrupt capability of a Computer Module is a logical generalization of the "trapping" feature found on several conventional computers. It permits the automatic interruption of a program, at the option of the program, when the computer module receives an "alert" that a condition requiring attention has arisen. It can be used to warn the program when an error of some type has occurred, minimize unproductive computer waiting time while another module completes its task, eliminate many programmed status test instructions and provide a convenient means of subjecting one computer module to the control of another. Program control of interruptions within a CM-400 is accomplished through the sense register S. This register may be filled with an interrupt