Error correction system in a programmable calculator

Abstract

An error correction system is particularly suitable for user programmable calculators which may be programmed to perform a series of functions on data entries by means of a series of program steps entered into the calculator from a storage media such as recorded magnetic cards or the like. Data is stored in one or more pairs of tracks on the recording media with the first track of each pair for storing binary zeros and a second track of each pair for storing binary ones. Each time a binary zero is present, an alternating transition negative to positive or positive to negative appears on the zero's track of the storage media and each time a one is present an alternating transition negative to positive or positive to negative appears on the one's track of the storage media. For reading the data stored on the storage media, means such as a data latch is provided for each track for storing the direction of the previous transition positive to negative or negative to positive for that track and means for comparing the direction of such previous transition with the direction of the present transition. Whenever it is determined that the state of a bit of data is missing on a pair of tracks, i.e., no transition stored on either track for a given bit, the transitions located prior to, and following said missing bit will indicate the track on which the data bit should have been stored and hence the state of the missing bit. In an embodiment in which at least two pairs of tracks are utilized, the ORed output from the first pair of tracks may be compared to the ORed output from the second pair of tracks such that whenever a bit appears for the first pair but not the second pair it is determined that a bit is missing for the second pair.