Patent GB-1011516-A (GB)
Title: Apparatus for generating or checking a parity digit
IPC: G06C25/00
Filed: 1964-06-12
Abstract: 1,011,516. Generating check symbols. NATIONAL CASH REGISTER CO. June 12, 1964 [July 16, 1963], No. 24543/64. Heading G4B. [Also in Division B6] A full keyboard calculating or accounting machine is provided with means for generating or testing a parity digit. Eight columns of keys are used for setting up calculations, the ninth column i being shielded by a removable cover 29. The stem of each key has three openings through each of which passes a nylon line 31a (for example). The openings in the stems are either circular, representing binary 1 or oval, representing 0, thus the openings corresponding to the number 2 indicate that 2 is represented by 010. In the embodiment shown 8 and 9 have the same representation as 1, 6 respectively. The lines 31a are connected to double pole, double throw switches 41, one switch being used for each bit. Operation of the key 2 in any column will throw over the centre switch of the group of three corresponding to that column but will leave the others alone. The switches corresponding to each bit position are connected in series as shown in Fig. 4. The upper portions of the stems of the keys 1-7 of the ninth column are each formed by an iron cylinder 26 connected by a plastic rod 50 to the lower part of the stem, Fig. 5.   The cylinders 26 form the cores of solenoids S1-S7 (S1 only shown). To generate a parity digit, a bar 95 is depressed and held in position by a lip on the casing. The required digit keys are then depressed and a parity digit is automatically set up in column i, so that there is an even number of bits in each position. If an odd number of ones appear in the first bit position, i.e. an odd number of the switches 42a-42h are actuated, current will flow from the source 60 through the coil 63 of a relay switch 64, through the switches 42a-42h and 47i (which remains in the state shown), through switch 58 to earth. Thus relay switch 64 will be actuated. If an even number of ones appear in this position, a circuit is not made and switch 64 is not actuated. The circuit to the coils S1-S7 passes through switch 72 and the set of switches 44i-44a corresponding to the third bit position, along lines 100 or 101, through one of the coils S1-S7, through the poles 67 or 68 of switch 64 and through the switches 43a-43i (second bit position) to earth. The arrangement is that one coil only is energized, this will operate its corresponding digit key, thus setting up a parity bit so that the total number of bits in each position is even. Depression of a bar 21 then operates the motor to print the number and its associated parity bit as shown in Fig. 1. If the number of bits in each position is already even as in the number 7542361 shown in Fig. 1, none of the coils S1-S7 is energized and a 0 parity bit is printed. The calculator shown is of the type that suppresses non-significant zeros but prints significant zeros when no key is depressed. It is suitably modified to prevent the suppression of zeros in column i. If it were of the type having keys for zero, then a further solenoid S0 sould be required. To check a parity digit, the cover 29 is removed and the parity digit key depressed with the other keys. In this instance bar 87 is depressed and locked in position as is bar 95. The circuit to the motor will then only be made if the parity is correct. If bar 95 is not depressed, the calculator may be operated in the normal manner, column i not being available for calculation however. If it is wished to define each digit uniquely, four switches must be provided for each key column, and two columns of parity digits would be required. U.S.A. Specification 1,386,021 is referred to.