Patent GB-1503567-A (GB)
Title: High speed printers
IPC: B41J1/20
Filed: 1975-02-25
Abstract: 1503567 Printers SPERRY RAND CORP 25 Feb 1975 [25 Feb 1974] 7725/75 Heading G4H In a printer, a non-printable character in a line of characters to be printed is identified and a selected printable character is printed in substitution for it. As disclosed, a type-band moves past a row of print hammers actuated under control of a print comparator comparing the outputs of a code buffer (holding the type-band character sequence) and a print line buffer (holding the line of characters to be printed), hammer actuations being counted in a match counter to signal completion of the line. Prior to this printing operation, a CPU supplies the following items in turn, those in brackets being optional depending on the mode of operation required (see below); a cartridge verification code, (a set of non-printable characters and corresponding printable duals), (a data check dual), a space code, the information to be loaded into the code buffer, the information to be loaded into the print line buffer. The cartridge verification code is compared with a code read from the type-band to verify that the type-band is the correct one, and a further bit to select a first mode (in which each non-printable character in the print line buffer results in a space in the printed line) or a second mode (in which those non-printable characters for which the CPU supplied corresponding printable duals have the latter printed instead of them, and the other non-printable characters have the data check dual printed instead of them). The space code is held in a register to specify which bit-combination will be used to specify "space". As the code buffer is being loaded, the codes are used to address an associative memory having one bit position per possible bit-combination, to set to "1" those positions corresponding to the contents of the code buffer (and thus, typeband). As the print line buffer is being loaded, spaces are recognized by comparison with the space register to increment the match counter (since spaces contribute to the length of the line). In the first mode, in addition, as the print line buffer is being loaded, the codes are used to address the associative memory, and the "0" bits found are counted by the match counter i.e. the non-printable characters in the line to be printed are counted into the match counter so that the latter will signal completion of the line once the printable characters have all been printed. The additional operations in the second mode, on the other hand, depend on whether or not the data check dual equals the space code. If it does, "0" bits addressed in the associative memory during loading of the print line buffer are counted into the match counter as in the first mode, and hammer actuations are produced, and counted in the match counter, not only in response to the print comparator comparing the outputs of the code buffer and the print line buffer but also whenever any one of the set of non-printable characters initially specified by the CPU (see above) equals the output of the print line buffer at the same time as its printable dual equals the output of the code buffer, pairs of registers being provided for the set and the duals, with further comparators. On the other hand, if the data check dual does not equal the space code, the "0" bits addressed in the associative memory during loading of the print line buffer are not counted into the match counter but instead are used to set tag bits at the corresponding positions in the print line buffer, and further hammer actuations (counted into the match counter) will be produced in addition to those above whenever the output of the code buffer equals the data check dual, provided the tag bit associated with the output of the print line buffer is set.