Patent GB-1181143-A (GB)
Title: A Cathode Ray Tube Character Display Apparatus
IPC: G09G1/18
Filed: 1967-03-08
Abstract: 1,181,143. Cathode-ray tube displays. INTERNATIONAL BUSINESS MACHINES CORP. 8 March, 1967 [8 March, 1966], No. 10806/67. Heading H4T. In a numeric C.R.T. display system in which the digits are built-up from combinations of bars from a figure-of-eight bar matrix augmented by a single central vertical bar for the digit 1, each bar is associated with a gate arranged, in conjunction with timing signals, to generate the bar, when opened, by unblanking the beam at the appropriate positions in a small T.V. type raster, which is moved sequentially to the different digit positions on the C.R.T. face. When a digit is to be displayed those gates corresponding to the combination of bars required are opened, each by a combination of binary signals representing the digit. The system also includes means for displaying decimal points, means for suppressing high order non-significant zeros and, in a modification, means for spacing the digits in groups of three starting at the decimal point. Decimal points.-A whole line of digits to be displayed is stored in a register 30, Fig. 3, each digit being coded by five bits the first of which indicates whether the digit is to be followed, on its lower denominational side, by a decimal point. Digits are read, highest denomination first, from the register 30, one by one into a five bit digit register 31. The digit is then decoded to open the corresponding bar-generating gates which, in one cycle of the system, generate the required digit. The small raster is then moved to the adjacent digit position and the next digit is displayed in a similar manner. If, however, any digit has a " one " bit in its first position indicating that it is to be followed by a decimal point, then after the digit has been displayed, the raster is moved on, read-out of the next digit from the main register 31 is inhibited, and a decimal point is displayed. That is, if a decimal point is required after any digit, an additional cycle, for the decimal point, is performed before the next digit is displayed. Suppression of high order zeros.-The digits are read from the main register 30 highest denomination first and each display is inhibited until a digit having at least one " one " bit present (which bit might be the decimal point bit). Thus, automatically for numbers less than unity, one zero is displayed immediately before the decimal point. Digit grouping with suppression of high order zeros.-In a modification (Fig. 8, not shown) digits above the decimal point are grouped in threes. This is effected by first circulating the multi-digit number from the main register 30, highest denomination first, through a processing arrangement which inserts a " one " bit into the decimal point position of each non-significant high order zero. The processed multi-digit number is then read from the main register 30 digit-by-digit into the five-bit digit register 31 starting with the lowest order digit. Digits are displayed, as before, but from right to left across the C.R.T., until a digit with a decimal point occurs. This decimal point, being the first, will be genuine and is displayed, in an additional cycle, as before, but before the accompanying digit is displayed. Display of further digits continues, but the digits are now counted and after each group of three a space is inserted (if desired a comma can be displayed). When eventually another digit occurs with a decimal point further display is inhibited because this decimal point, which is pseudo, will mark the beginning of the non-significant high order zeros.