Browse Prior Art Database

Keystroke Intercept Circuit

IP.com Disclosure Number: IPCOM000051716D
Original Publication Date: 1981-Mar-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 50K

Publishing Venue

IBM

Related People

Floyd, RE: AUTHOR [+4]

Abstract

The keystroke intercept circuit is used in the computer-aided terminal scanner described in [*] to capture or inject keystrokes at the keyboard screen interface of a terminal. This circuit is computer-controlled by a system not associated with the terminal attached to the intercept circuit. The keystroke data captured or injected by the intercept circuit is stored in a fixed medium, such as tape or disc, by the computer control system. The intercept circuit has two modes of operation: record mode, or keystroke capture, and playback mode, or keystroke injection.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 52% of the total text.

Page 1 of 3

Keystroke Intercept Circuit

The keystroke intercept circuit is used in the computer-aided terminal scanner described in [*] to capture or inject keystrokes at the keyboard screen interface of a terminal. This circuit is computer-controlled by a system not associated with the terminal attached to the intercept circuit. The keystroke data captured or injected by the intercept circuit is stored in a fixed medium, such as tape or disc, by the computer control system. The intercept circuit has two modes of operation: record mode, or keystroke capture, and playback mode, or keystroke injection.

The figure shows the circuit in full detail. Signal names, beginning with KBD or CRT, are part of the terminal's keyboard/screen interface. Signal names beginning with ICT are generated by the computer control system. The keyboard/screen data, strobe, and lockout signals are connected to the keystroke intercept circuit; all others are fed-through.

In the record mode, the +ICT PLAYBACK signal is inactive, and all keyboard data lines (+KBD DATA IN) and strobe line (-KBD STROBE IN) are routed to the cathode ray tube (CRT) through multiplexer 1. In this mode, keystroke activity between the keyboard and the screen is not affected. The keyboard data lines are latched and stored by polarity hold latches 2 by either -KBD STROBE IN signal going active or one of the +KBD DC KEY signals changing state. This action holds the state of those signals for recording by the control computer. The +KBD DC KEY signal is defined as a keyboard data line whose state causes changes on the screen, that is, the reset line going active without the strobe line going active.

The KBD DC KEY signal is detected by edge detect circuit 3 and the output of edge detect circuit 3 and the -KBD STROBE IN signal are applied to the inverting inputs of OR gate 4, the output of which is applied to the clock input of latches 2. The -KBD STROBE IN and KBD DC KEY signals also set either of the flip-flops 5 and 6, respectively, and the output signals from those flip-flops are applied through OR gate 7 to provide the +ICT HIT signal, which indicates to the control computer that a keystroke has been captured and is ready for recording. When the control computer reads latches 2, it sends back the -ICT CLEAR signal and resets flip-flops 5 and 6, thereby ending the +ICT HIT signal.

If the screen has a keyboard lockout signal (IBD LOCKOUT IN), it is provided through OR gate 8 with the +ICT HIT signal causing the KBD LOCKOUT OUT signal to block all further keystroke activity until the recorded keystroke is read and cleared by the control computer. If the keyboard lockout signal is not available, the control computer must record keystrokes at a faster rate than they are being entered on the keyboard. In this case...