Patent GB-1442856-A (GB)
Title: Desk-top electronic computer with mos circuit logic
IPC: G06F15/78
Filed: 1973-07-16
Abstract: 1442856 Electronic computer ING C OLIVETTI & C SpA 16 July 1973 [14 July 1972] 33686/73 Heading G4A An electronic desk top computer has a logic unit formed on three semi-conductor circuit chips each having a timing circuit, the timing circuits being interconnected, and the chips being interconnected by a single data and address line. The calculator which is a microprogram controlled device is described in some detail. Briefly however it includes a keyboard and printer connected to logic circuits disposed on three MOS chips. The first chip includes a microprogam store together with addressing logic and a timing circuit, the second includes an arithmetic and logic unit and a timing circuit, and the third includes input/output interfaces, control logic and a timing circuit. Timing.-The calculator handles four bit BCD coded 25 character words in bit serial fashion. An oscillator supplies a clock signal from which two opposite clock pulses are generated by a flip-flop. These signals are fed to a timing circuit on the control chip which includes a circuit including inverters and FETs to generate a series of regular clock pulses # 1  and # 2  which in turn control two counters, a bit counter producing a single binary one on one of four outputs to indicate the bit and a series of 25 coded five bit signals indicating the character. The other two chips contain similar timing circuits arranged to produce similar coded signals but delayed by 20 bits. Programming.-The microprogram memory on the program chip is addressed by serial data fed from a buffer register under the control of the timing pulses. The buffer register may be loaded from the keyboard, by incrementing the previous address, or modifying a previous address. Four types of address modification or "jump" instructions are described. Each micro-instruction is of eight bits, three of which are used to indicate the type of jump. In the first the remaining five bits of the instruction specify the jump address, which thus lies in a restricted range of store addresses. In the second two microinstructions are used to perform a conditional branch. If the condition is satisfied eight bits of the instructions are used on the jump address thus providing a larger range. In the third two microinstructions are used to perform an unconditional jump to a ten bit address which enables the jump address to lie anywhere within the microprogram store. The fourth type is similar to the third except that the old address is retained for a subsequent return. The addressed instructions are read from the microprogram store, buffered, and fed serially under the control of timing signals to the logic and/or control chips over the same line as the address was fed to the store for decoding. Logic.-The logic unit includes registers A. M. R. T1, T2, all registers being formed by shift registers recirculating under the control of timing pulses, and a conventional two stage serial adder arranged to add filler bits as appropriate. Several circuits including inverters and NAND gates are described for transferring data from one register to another, shifting data within a register, adding the contents of two registers, and incrementing the contents of a register. Fixed and floating point arithmetic and rounding operations are described. The printer is controlled by comparing the character under the print hammer with the desired character to actuate the hammer.