Patent GB-888023-A (GB)
Title: Table lock-up system for a data processing device
IPC: G06F9/30
Filed: 1960-02-10
Abstract: 888,023. Selecting digital data. INTERNATIONAL BUSINESS MACHINES CORPORATION. Feb. 10, 1960 [Feb. 11, 1959], No. 4722/60. Class 106 (1). A table look-up operation comprises comparing the contents of storage locations with the contents of a register and, on a predetermined relationship between a data word and the register contents being found, placing the data word in the register. A high-equal search is started by entering a search argument in accumulator 3 and by an instruction word of which the first three positions, sign and operation code, are staticized in register 10a and the last four positions, specifying the address of a record control word, in register 100. Interpretation of the operation code in matrix 14 leads to the activation of a table look-up control ring 17, and to the setting of a request latch 34 and a data ring 43. A particular location in memory contains the amount by which the address of a data word being examined is to be incremented to obtain the next data word, and this location is generated in response to a signal on line 15c from the matrix 14 in address generator 18. The address of the record control word (RCW) is transferred from register 100 to register 102; the increment value is transferred from memory to register 100. The RCW containing start and stop addresses defining the search area is then taken from memory and staticized, the start address in auxiliary register 30b, the stop address in register 30c. The start address is fed through adder entry B and the adder to comparing unit 30a, followed by the stop address via entry A. If the start address is higher than the stop address switch 40a will operate error indicating means, but if lower the start address will be gated from register 30b to register 70 and thence to the memory address register 2. The first data word will then be transferred to arithmetic register 80 and to the adder 190 by entry B concurrently with the search argument from accumulator 3, 160, by entry A. If the comparison signal is low the next data word is called for by entering concurrently the increment value from register 100 to the adder by entry B and the start address from register 30b. The sum is transferred on line 196 to the register 30b as a new start address, compared with the stop address, and if lower, the process is repeated of calling for the data word at the start address, comparing it with the search argument and, if necessary, computing the next start address. If a data word is higher or equal to the argument, the address in register 30b specifying the location of the word is transferred together with the increment value to the storage position initially containing the increment value. If the search field contains several blocks of data words scattered through the memory, with each block is associated an RCW. If during a search the start address is found to be greater than a stop address the sign of the RCW is examined and if positive the address of the next RCW, the address of the present RCW plus one, found in address register 102 is used to transfer the new RCW from memory to register 30b, 30c. If the sign is negative the search is complete. A low search may also be made to find the minimum value lower than the search argument. In this case as a value is found it replaces the search argument in accumulator 3 and the search is continued. The address of found value is stored in accumulator 2. Portions of data words may be searched if an appropriate code is entered in two positions of the original instruction word that are then staticized in register 10c. The memory, adder and registers are not described in detail but are of magnetic cores. The register may receive or transmit information in parallel or serial form and may be right- or left-shifted. Transfer of information from memory to a register takes at least two cycles since the information is staticized in the bus by means of capacitors (Fig. 9, not shown) and is then transferred to the register. U.S.A. Specification 2,959,351 is referred to.