Fixed word storage arrangement with interpolation facilities

Abstract

Abstract 1444819 Interpolator SIEMENS AG 19 Dec 1973 [23 Jan 1973 25 May 1973] 58719/73 Heading G4A [Also in Division F1] The value of a function Z of one or more independent variables is obtained for values of the variable(s) by interpolation using values of Z for certain possible values of the variable(s) stored in a read only memory. The arrangement is for controlling an internal combustion engine, see Division F1. Signals x 0 and y 0 representing engine speed and throttle setting are fed to A-D converters 29 and 30. The most significant bits MSB(x 0 ), MSB(y 0 ) of the resulting digital words x 0 , y 0 are used together to address a read only memory 24 storing the values of a function Z = F (x, y), e.g. ignition timing data for the engine, for those values of x and y given by all the combinations of the most significant bits of x and y. A counter 28 has a number of bit positions equal to the number of the remaining least significant bits of x 0 and y 0 , LSB (x 0 ), LSB (y 0 ) and is incremented through a complete cycle for each interpolation. For each value of the counter contents the least significant bits of x 0 and y 0 are compared with respective groups of bits in the counter. If the least significant bits are greater than their associated group of counter bits the corresponding most significant bits are incremented by one and used to address the memory 24. If the least signaificant bits are less than or equal to their associated group of counter bits the corresponding most significant bits are used unchanged to address the memory 24. The values of Z read out of store 24 are accumulated in register 21, the final contents of the register being divided by the number of values through which the counter contents have passed, e.g. by a shift operation, to give the final interpolated value of Z for the input values of x 0 and y 0 . The final value of Z is fed to a D-A converter 21 whose output is used to control the engine. In a modification two read only memories are provided storing ignition timing and fuel injection duration, the two memories being used alternately to provide data to control the ignition timing and fuel injection duration. The arrangement may also be used for functions of three (or more) variables.

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