Patent GB-1143327-A (GB)
Title: Improvements in electronic digital computers
Inventor: TAUB DANIEL MATTHEW
IPC: G06F3/0489
Filed: 1967-06-15
Abstract: 1,143,327. Computers. INTERNATIONAL BUSINESS MACHINES CORP. 15 June, 1967, No. 27720/67. Heading G4A. An electronic digital computer produces display control signals defining different display formats in response to signals indicating that different classes of instructions are being performed, the display control signals being impressed on a radio frequency carrier wave for application as a modulated input to a television receiver. The computer, usable for teaching, has a capacitive touch keyboard, core store, addersubtractor, television receiver display and magnetic tape input/output. The core store has 222 words, each of eight 4-bit characters. Words 0-99 are available to the user to store data and instructions, words 100-221 being reserved for general-purpose registers (including modifier registers) and subroutines. The store can be addressed according to word and character within word from either of two address registers, a common increase/decrease unit being provided to increment of decrement the character portion of the address in the address register used. Two general-purpose registers are of double length i.e. two words each, the addresses of the two words being ten word positions apart in each case-in these cases a carry out of the character address portion from the increase/decrease unit increments the tens digit of the word portion of the address register to reach the second half of the double-length register after accessing of the first half has been completed. A word in store may contain a signed floating-point binary-coded-decimal number, or two basic instructions, or one macroinstruction. There are two types of basic instruction, viz. (a) register instructions which operate only on the contents of registers and specify register number(s), (b) single address instructions specifying a store base address (or rather the units and tens digits of the word portion of the base address, since the user is limited to words 0-99). A macro-instruction specifies three store base addresses similarly. The keyboard has keys for 0-9, decimal point and minus for entering operands, addresses and instructions via a keyboard register, and control keys to clear the keyboard register, load a store address register from it, increment the address by one, load the store from the keyboard register, run the computer under programme control, dump the store contents on to magnetic tape, read the tape again and compare it with store as a check, reload store from the tape, stop, and select modes of operation implied by the preceding including whether instructions are to be taken from store or keyboard register in the case when the computer is being run under programme control. The computer will also stop after executing input and output instructions, and on detection of error. Three further keys cause the computer to stop at any or all of three stages in the execution of each macro-instruction (executed by a sequence of basic instructions forming a subroutine) and of each basic instruction (unless part of the execution of a macro-instruction). The possible stopping stages for a basic instruction are (A) after the instruction has been fetched and entered into an instruction register, (B) when the true addresses of the operands have been determined, (C) when the instruction has been executed and the instruction address register has been incremented. The stopping allows the operator to see the state of the computer on the television display which shows the contents of the instruction address register, the keyboard register, the instruction register, indications of mode, error (present/absent), stopping stage, the contents of a link register used in branching to a subroutine to execute a macro-instruction, the contents of storage locations and other registers (including operands) flanked by the addresses and identifiers of the locations and registers respectively, and the state of a latch indicating whether a macro-instruction is being executed. Which of these displays occur depends to some extent on which of the three classes of instructions the instruction being executed belongs to. Apart from the check possible after dumping store to tape, detection of overflow and invalid instruction errors are also mentioned.