Browse Prior Art Database

Keyboard Overrun Control

IP.com Disclosure Number: IPCOM000082197D
Original Publication Date: 1974-Oct-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 54K

Publishing Venue

IBM

Related People

Duggan, CJ: AUTHOR

Abstract

An overrun error system detects when a keyboard, attached as an input/ output (I/O) device to a computer system, is operated successively, whereby servicing of the first keystroke is not completed prior to the operation of a second keystroke. Such a condition may occur when two or more keys are struck simultaneously, or when keys are struck at a rate exceeding the servicing rate. The overrun error system includes provisions for notifying the keyboard operator of the overrun condition and for error recovery.

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Keyboard Overrun Control

An overrun error system detects when a keyboard, attached as an input/ output (I/O) device to a computer system, is operated successively, whereby servicing of the first keystroke is not completed prior to the operation of a second keystroke. Such a condition may occur when two or more keys are struck simultaneously, or when keys are struck at a rate exceeding the servicing rate. The overrun error system includes provisions for notifying the keyboard operator of the overrun condition and for error recovery.

Microcode contained in storage 10, Fig. 1, is accessed by central processing unit (CPU) 20 to provide keyboard enabling signals to keyboard attachment 30. Whenever any key on keyboard 50 is operated, a KYBRD GATE signal is generated. This signal sets latch 31 and thereby causes an interrupt to CPU 20. This signal also loads register 32 with data from the keyboard via bus 51. Additionally, this signal sets data gate latch 33. The keyboard operator is aware of the key depression, because latch 38 is set by an Enable KYBRD signal from command decode logic 35 when keyboard 50 is enabled by a command issued over data bus out (DBO) 21, along with proper control signals on control bus 22.

The setting of latch 38 causes AND circuit 40 to be conditioned via inverter
39. A KYBRD FIRE CLICKER signal 42, generated internally in keyboard 50, is passed by AND circuit 40 in attachment 30 back to keyboard 50 to fire a magnetically operated clicker located therewithin. The noise of the clicker signals the operator that a key was depressed.

The interrupt signal from latch 31 passed to CPU 2O causes entry into a microprogram for examining the contents of register 32. This is accomplished by issuing a command over DBO 21 and providing proper controls on control bus 22, whereby logic 35 generates a SENSE KYBRD REG signal which is applied to AND circuit 36. AND circuit 36 is representative of a group of AND circuits, one for...