Patent GB-1108401-A (GB)
Title: Digital character generator and display unit
IPC: G09G1/10
Filed: 1966-03-01
Abstract: 1,108,401. Cathode-ray tube displays. SPERRY RAND CORPORATION. 1 March, 1966 [1 March, 1965], No. 8944/66. Heading H4T. In an arrangement for tracing Alpha- Numeric characters on the screen of a cathoderay tube beam positioning means operates to step the beam cyclically through a plurality of positions on the screen, a memory stores digital data signals indicative of individual characters to be traced and a register coupled to the positioning means and to the memory selects data signals corresponding to a desired character which by means of a further register causes a particular character generator to respond and operate to cause the beam to trace the particular character at the required position. The character indicative signals may be derived from a computer and/or from a keyboard and information composed by the latter may be fed to the computer. Facilities are provided for effecting an operation at any of the positions to which the beam is stepped, such position being selected by key switches which cause a distinctive trace in the shape of an inverted " L " (Fig. 9, not shown) termed a " cursor " to be produced. The operation at such selected position may then consist of the tracing of a character, if the position is vacant or, if it is occupied by a character, the deletion of such character from the display and from the memory followed, if required, by the insertion of a new selected character or the insertion of a character without deletion of the existing character. When a character is deleted and not replaced by a new character the positions of the following characters in both the display and the memory are all shifted to the left by one character position whilst when a character is inserted without deleting an existing character the following characters are all shifted by one position to the right. In the particular embodiment described the display, although not so limited, may consist of up to 512 characters arranged in 16 lines each of 32 characters and for this arrangement a 512 word, 6 bit, core memory is utilized. The character generator comprises a plurality of diode matrices such that the sequential energization of the elements in a selected matrix produces digital output signals for controlling the X and Y beam deflections and the beam intensity of the display tube for the tracing of a single character [Figs. 7a, 7b, 19a, 19b, not shown). Composite arrangement.-The general arrangement is shown in Fig. 1, and further detailed in Figs. 20a and 20b. Thus, the General Address Control 6 operates to position the beam sequentially in each of the 512 character positions utilizing push-pull electromagnetic deflection, to control the insertion, read out and deletion of characters in the memory and to allow the cursor to be positioned as desired without (unless desired by operating special function keys) affecting the existing display or the memory content. All operations are controlled by a timing unit 2 such that all input-output actions, i.e. the operation of the various registers themselves and their effect on the memory, sequential beam stepping, cursor production and character generator selection &c. in response to input commands from the computer or the keyboard or other switch devicesoccur during alternate intervals of 16 Ás whilst the actual result of such commands-i.e. the tracing, insertion and deletion &c. of characters occur during intervening 16 Ás intervals. For the sequential beam stepping the various stages of the M register, which stores the X and Y components in binary digital form, are connected to the deflection coils via amplifiers (which may be Miller integrators) weighting resistors and transistor drive amplifiers performing a binary-to-decimal transformation (Fig. 12, not shown). Since the line fly-back period is greater than the 32 Ás cycle period the registers are operated to allow the character tracing motions to occur twice whilst blanking the beam during the tracing which occurs in the fly-back period. For the actual character tracing digital signals representative of successive X and Y coordinates and for beam brightness and blanking control, which are derived by sequential energization (during the 16 Ás trace period) of the appropriate character matrix (Fig. 7b, not shown), are applied via a control circuit (Fig. 8 and Fig. 10, not shown) including binary weighting resistors and transistor drive amplifiers to the push-pull electrostatic deflection plates of the display tube and to the intensity control electrode the latter being operated in accordance with the trace length to maintain uniform brightness. The circuit of Fig. 8 (not shown), also includes means which in response to certain ones of a sequence of pulses derived from the timing unit (Fig. 1a not shown) during the 16 Ás trace period (prior to character tracing) operates the deflection and intensity control electrodes firstly to move the beam (whilst blanked) from X = 0, Y = 0 to X = 2, Y = 3 preparatory to tracing the cursor. Other pulses of this sequence then cause the beam to trace the cursor by deflecting it (blanked) to X = 0, Y = 7 and then (unblanked) to X = 5, Y = 7 and thence to X = 5, Y = 0 (Fig. 9, not shown). The various steps involved in tracing the character " Q " are depicted in Fig. 7C (not shown) and the actual deflection waveforms involved in Fig. 10a (not shown). The specification includes a detailed account of the operation of the arrangement as a whole and of the construction of the various registers and other circuit elements utilized.