Browse Prior Art Database

Controlled Switch-Matrix Keyboard

IP.com Disclosure Number: IPCOM000043875D
Original Publication Date: 1984-Oct-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Holloway, WL: AUTHOR [+2]

Abstract

Only one drive line of a plurality of drive lines from a microprocessor to a switch-matrix keyboard is configured as an output from the microprocessor at any time while all of the other drive lines are configured as inputs. This eliminates possible damage due to short circuiting of the drive lines when they are output drive lines if two keys are depressed simultaneously. This eliminates the need for a decoder between the microprocessor and the keyboard as has been previously required to prevent shorting of two output drive lines of the microprocessor.

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Controlled Switch-Matrix Keyboard

Only one drive line of a plurality of drive lines from a microprocessor to a switch- matrix keyboard is configured as an output from the microprocessor at any time while all of the other drive lines are configured as inputs. This eliminates possible damage due to short circuiting of the drive lines when they are output drive lines if two keys are depressed simultaneously. This eliminates the need for a decoder between the microprocessor and the keyboard as has been previously required to prevent shorting of two output drive lines of the microprocessor. A switch-matrix keyboard 1, which may have membrane switch arrays as its switches, is connected to a microprocessor 2, which has bidirectional input/output pins that may be configured as inputs or outputs under control of a software program, through drive lines 3 and sense lines 4. When a key on the keyboard 1 is depressed, a switch is closed to cause a low signal to be supplied over one of the sense lines 4 to the microprocessor 2 to indicate the key that has been depressed. The drive lines 3 are controlled by the software program of Fig. 2 which has all the drive lines 3 initially as inputs. Then, one of the drive lines 3 becomes an output and all of the sense lines 4 are read. If any of the sense lines 4 is low, this shows the depression of a specific key on the keyboard 1. After the sense lines 4 have been read, all of the drive lines 3 are returned to inputs and the next of th...