Patent GB-1491718-A (GB)
Title: Automatic writing systems and methods therefor
IPC: B41J5/42
Filed: 1974-10-31
Abstract: 1491718 Control of printers; data processing; recording on magnetic media XEROX CORP 31 Oct 1974 [2 Jan 1974 (2)] 47135/74 Heading G4H In an automatic writing system comprising keyboard, printer, buffer and other recording peripherals 1, 4, 17, 18 connected by a common data bus 19, data is always transmitted from one peripheral to another via a character register M. Register M performs a holding function so that each data character introduced on to bus 19 for processing and storage may be inspected so that any necessary data processing may be performed by a microprocessor 16 containing the register prior to forwarding of the character to a destination peripheral. Alphanumeric, format and function data may be entered at keyboard 1; its presence is indicated to the microprocessor on a common status bus 21, whereupon program control is initiated using a common instruction word bus 20, the degree of completion of a command issued to a peripheral being indicated on bus 21. Data from keyboard 1 may be recorded in peripheral 18 which, as described, is a magnetic cassette unit, and data from a tape here may be printed or re-recorded, possibly with additions or revisions made using the keyboard. Microprocessor 16 (Figs. 20-24, not shown) also comprises an arithmetic unit 84 used, inter alia, to test data from keyboard 1 for print and non-print characters and to add a parity or "longitudinal redundancy" bit (obtained by XORing each bit of a character with the corresponding bit of the next character) to data being recorded at 18 (and to carry out a comparison check between the bits of data to be recorded and the bits of data actually recorded). A pre-programmed read-only memory 80 is controlled by an address register 81 which receives the status indications on bus 21. ROM80 may be a hard wired magnetic memory storing 4,096 instruction words B 0 -B 15  and may be a 3-D array of MS1 chips divided into 16 "major pages" each containing 16 "minor pages" containing the instruction words. Each address A 0 -A 11  applied to ROM80 from register 81 is also fed to a return address register 82 which provides a branch and return facility (up to four for each addressing sequence). Bits A 0 -A 7  are also fed back to register 81 whereby a new address (incremented by one) is applied as the next address for ROM80. Microprocessor 16 initially goes through an idle program when it selectively samples a plurality of status conditions at each peripheral in sequence; the program branches accordingly when a signal appears on bus 21. Buffer 17 (Fig. 8, not shown) comprises identical recirculating shift registers 35, 36 each acting to store information received one character at a time from bus 19 until a whole line has been accumulated (indicated by a CR character), whereupon the entire contents of register 35 may be fed to peripheral 18 while the contents of register 36 may be used for additional processing (register 35 stores data from any peripheral; however, register 36 is not employed to store data from keyboard 1, nor is data therefrom generally recorded at 18). Printer 2 (Figs. 3-4, not shown) may be a "daisy wheel" printer using a (possibly twocoloured) carbon or cloth ribbon and being capable of printing lines alternately from left to right and from right to left. Automatic and manual margin control facilities are provided. The printer receives 7-bit ASC11 code and 11-bit control characters (carriage position, paper index). The ribbon may be lowered to enable the printed line to be read. The duration of print-hammer energization is controlled to compensate for different character sizes. Keyboard 1, Fig. 5 (and Fig. 7, not shown) incorporates conventionalupper/lower case alpha numeric keys, "encoded function" keys (alphanumeric keys plus code key 220) for ERASE, &c., and "mode control" keys 229-232 for RECORD, DUPLICATE, &c. Some keys may be typamatic, and the mode keys are illuminated when depressed. Depression of each key produces an 8-bit ASC11 code (BCD code mentioned as an alternative) whose msb. indicates whether a print or a non-print function has been selected. Alternatively, a capacitively coupled and coded keyboard may be used. Magnetic tape unit 18 (Figs. 9-11, not shown) contains separate "read only" and "read/write" sections 54-56 and 50-53. As described the unit takes cassette tapes travelling at 20 in./sec. (fast wind at 70 in./sec.) on which data is recorded at 400 bits/inch (1000 characters/sec.) by any conventional technique (biphase, NRTZ, &c.) The data is arranged in "blocks" of "lines" on the tape, these corresponding most conveniently to pages and lines of printed data. Each line is recorded with 50 redundant character spaces to allow for subsequent expansion during revision, the parity or redundancy code, and an interline gap. Each block is provided with an address (which can be set on thumbwheels 233 on keyboard 1 and which is displayed) and a (longer) interlock gap. Each record on the tape is followed by an "end of record" mark and a (very long) EOR termination gap (Figs. 12A-12C, not shown). Data is recorded on the tape in whole lines (using buffer 17) to avoid having to continually start and stop the tape. Data to be recorded is conveyed in parallel along bus 19 and converted to serial form for recording. Alternatively, bit-parallel recording may be used if the unit is a multitrack tape, disc or drum instead of the cassette. Magnetic cards may also be used. Operating modes (Figs. 13-19, only Fig. 17 shown).-These are (a) PRINT: the system is operated as a typewriter. (b) RECORD: information entered at the keyboard is printed and recorded on tape (using register 35 and section 50-53). (c) PLAY: data is read from one or more tapes and printed; it may be merged with data from the keyboard (e.g. using a "skip" key) to produce a revised document. Two tapes may be used (with an "alternate reader" key) with the keyboard to prepare batched letters. (d) REVISE: minor revisions (which can be included within the space of one line plus its 50 character spaces) are carried out using registers 35, 36; the revised data is printed and rerecorded on the original tape. (e) TRANSFER (Fig. 17): Major revision or editing operations are performed on data on the tape read at 54-56 using registers 35, 36 and keyboard 1. The revised data is printed and recorded at 50-53. (f) DUPLICATE: one tape is copied on to another without alteration. (g) SEARCH: A block address is set on thumbwheels 233 and compared with block addresses obtained as the tape is wound forwards or backwards at 70 inch/sec. In the above, whenever revised data is printed a two colour ribbon may be used so that old and new text may be readily distinguished.