Patent GB-795365-A (GB)
Title: Improvements in or relating to electronic digital calculating equipment
Inventor: BIRD RAYMOND
IPC: H03M7/08
Filed: 1955-11-11
Abstract: 795,365. Digital electric calculating apparatus. BRITISH TABULATING MACHINE CO., Ltd. Nov. 8, 1956 [Nov. 11, 1955], No. 32291/55. Class 106 (1). In Specification 777,244 there is described a device for converting a number encoded on a record card by perforations in columns to represent the digit in corresponding decimal denominations, to a binary-coded serial pulse train. For this purpose a magnetic drum is provided with a track having sixteen words each of thirty-two digits in which is recorded in succession the binary equivalents of ascending powers of ten. Thus the first word representing 10‹ has a binary " 1 " and thirty-one " 0 "s, the second (10<SP>1</SP>) has " 1010 " and twenty-eight " 0 "s and so on. The card sensing brush for each column controls a trigger connected to a gate, the gate being conditioned by a signal from a decoding matrix when the decimal equivalent word on the drum corresponding to the column is being read out, allowing this word to pass into an accumulator if the brush controlled trigger is set. Thus while each row of the card is sensed the drum makes a complete revolution and the decimal equivalent corresponding to columns in which a perforation has been sensed is entered into an accumulator, the equivalent being entered not only during the row in which it was sensed but in subsequent rows until the end of the sensing cycle. Thus for a hole in the eight position of the hundreds from the drum column, one hundred is entered eight times into the accumulator. Since the card sensing device and the drum are not synchronized to make sure that a complete set of conversion equivalents are presented in each index position the drum must make two whole revolutions for each card index position. The present invention avoids this necessity and reduces the revolution of the drum to a maximum of one and a quarter for each card index position. To this end there is provided a source of signals corresponding in time to predetermined fractions of a revolution of the drum 1, means for counting these signals which produce an output on a count equal to a full rotation, means for gating the signals to the counting means and control means rendered operative by a fraction signal and rendered inoperative by the output signal to control read out of a full set of conversion equivalents from the drum. The fraction signals may be pulses recorded on the drum, for example each quarter of a revolution, but in the form described clock pulses, one for each of the thirty-two digit positions of the sixteen words, are fed to gates 3 and 11. Trigger 2 is set by an end-of-revolution signal to pass the pulses to counter 4 which counts up to thirty-two and emits a signal to the word counter 5 having four binary stages counting up to sixteen. The carry output from the second stage which occurs at each quarter of the full count, is taken to gate 6. This signal which is called a "fraction signal " is allowed to pass through the gate 6 when it is opened by trigger 8 controlled by a pulse at each card index position from the card sensing mechanism. The first fraction signal after the card index position pulse passes to gate 13 and a trigger 10 which controls it so that the gate is closed until the trigger has been set by the first pulse. Subsequent fraction signals passing through gate 6 also pass through gate 13 to counter 9. This counter counts up to four, which corresponds to a full revolution, and the output then unsets trigger 10. The set output of trigger 10 also controls gate 11 to allow clock pulses from the drum to pass to the read out control. These pulses therefore pass for the length of time the trigger 10 remains set, i.e. for one revolution. These clock pulses are gated with the read out from the decimal equivalents as in the earlier case and the resulting signals entered into the accumulator.