GB1368834A - Selective printing apparatus - Google Patents

Abstract

1368834 Printers INTERNATIONAL BUSINESS MACHINES CORP 1 May 1972 [13 May 1971] 20054/72 Addition to 1368507 Heading G4H In a modification of printing apparatus as in the parent Specification, a character is replaced in a store by an inhibiting signal when it has been printed. A tape chain moves a row of hammers spaced along the print line During each of a series of scans (a scan being divided into three subscans), each hammer in turn is aligned with one (a respective) type element, in a set option time for that hammer, each set option time being followed (before the next set option time) by a reset option time for another hammer, such that almost 2/3 of a scan occurs between the set option time and the next reset option time for a given hammer. A line of characters to be printed is supplied by a CPU on bus 176 to a print buffer 156A. A chain image store 156B indicates the characters on the type chain Rotation of a slotted drum, with the type chain, is sensed at 152, to drive a subscan counter 184 and a character (i.e. scan) counter 186. Registers DAR, IAR, RAR are initialized and updated during operation by ALU 162 fed from character counter 186, and logic (including OR 252) at the bottom left in Fig. 3, except that DAR is initialized from the CPU over bus 176 For a set option time, DAR addresses the print buffer 156A via MAR to load character into a register X, the contents of MAR also being placed in HAR to select a hammer driver via decoder 174 (which controls gates 210, 212 at the bottom right of Fig 3) The IAR addresses chain image store 156B via MAR to load a character into register Y. Registers X, Y are compared in ALU 162 and if equal, produce a "compare" signal which sets a latch 206 in the appropriate hammer driver via the gate 210 selected by decoder 174. The "compare" signal controls AND 236 (at left in Fig 3) to write an invalid character in place of the character just printed in print buffer 156A. For a reset option time, RAR addresses print buffer 156A via MAR to load register X, the contents of MAR also being placed in HAR to select a hammer driver via decoder 174. The selected hammer driver is reset via AND 224 (middle bottom of Fig 3), provided that the invalid character is not recognized in register X by AND 234 (middle bottom of Fig. 3), each recognition inhibiting the hammer reset and, via AND 238 (middle left of Fig. 3), replacing the invalid character in print buffer 156A by a character which will not satisfy AND 234. Thus a hammer driver, once set, will be reset about 1 2/3 scans later rather than 2/3.