GB1370654A - Keyboard with roll-over feature - Google Patents

Abstract

1370654 Keyboards PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 11 Nov 1971 [14 Nov 1970] 52407/71 Heading G4H A keyboard enters data into a store, keyentered data being compared with previous key-entered data in the store, to permit output from the store in the event of non-correspondence. The invention deals with the roll-over problem. In a first embodiment, the keys are repeatedly interrogated in turn. The identity of an actuated key is encoded and inserted into a first register, and the contents of this register are compared in parallel with those of second, third and fourth registers. The registers are shifted so that the contents of the first to third registers are transferred into the second to fourth registers respectively. If none of the comparisons showed equality, the contents of the first register are also gated to an output (to a computer) during the shifting. The last key is a rest key, the identity of which is encoded, &c. as above, if no other key is actuated in the current interrogation cycle. If a key is actuated too soon after the previous key, the interrogation is stopped or output to the computer is blocked, and an error display indicator is actuated. The interrogation may be slowed while an actuated key is being processed. A second embodiment differs in that there are 14 data keys and 2 rest keys arranged in a matrix and interrogated by rows and columns in response to detection of key-actuation which causes production of (16-n) interrogation clock pulses plus a reset pulse, where n is the number of currently-actuated keys, release of keys also being detected so that n is known (so that a rest key is not always reached in the interrogation). Comparison is serial-by-bit with recirculation of the registers (of which there are three), and gating out to the computer is parallel by bit. A bi-stable reset on detection of key-actuation, and set on gate-out to the computer, prevents such gateout when set so that only one key-identity can be passed to the computer per interrogation cycle, with the result that each key-actuation results in only one input to the computer. An error signal is produced if three keys are in the actuated state together. If a key is actuated while the (16-n) pulses mentioned are being produced in response to a previous key, interrogation stops and an error signal is displayed. A third embodiment differs from the first in having no rest key, interrogation commencing in response to each actuation or release of a key, the number of depressed keys controlling the distance along the sequence of registers that the key-identity is shifted, the contents of the first register being also retained by recirculation. Only one keyidentity can be passed to the computer per interrogation cycle.