Browse Prior Art Database

Dynamic Link Library for Recognizing Multiplexed Keystrokes

IP.com Disclosure Number: IPCOM000111435D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 98K

Publishing Venue

IBM

Related People

Marik, MD: AUTHOR [+3]

Abstract

Disclosed is a Dynamic Link Library (DLL) in a host computer to handle all communications with a signal transfer unit. The signal transfer unit multiplexes keypad keystrokes from a number of remote units, for transmission to the host computer, where the keystrokes are decoded by the DLL.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Dynamic Link Library for Recognizing Multiplexed Keystrokes

      Disclosed is a Dynamic Link Library (DLL) in a host computer to
handle all communications with a signal transfer unit.  The signal
transfer unit multiplexes keypad keystrokes from a number of remote
units, for transmission to the host computer, where the keystrokes
are decoded by the DLL.

      The Figure is a schematic diagram of a system to permit the
remote viewing of segments of motion pictures at a number of remote
viewing units 2, each of which includes a viewing screen 4 and a
keypad 6, through which the user can provide input information to the
system.  The operation of the system is controlled by a host computer
8.  A signal transfer unit 10 is connected between the remote viewing
units 2 and host computer 8, to overcome the limitation associated
with the number of communication ports available at host computer 8,
by multiplexing the keypad keystrokes from remote viewing units 2
into a single communication port 12.  The software operating in host
computer 10 includes application programs 14, which control operation
of the system, and a DLL 16 interfacing with data transmitted through
communication port 12.

      Each remote viewing unit 2 is physically connected to signal
transfer unit 10 through a standard RS485 interface, using two wires
for receive and transmit functions.  In signal transfer unit 10,
these two wires from each viewing unit 2 are multiplexed into one
UART, along with signal lines from host computer 8.  The UART is
controlled by control logic of the signal transfer unit 10.

      The communication protocol used between signal transfer unit 10
and each remote viewing unit 2 is a very simple, single-byte command
structure.  Signal transfer unit 10 requests new keypad keystroke
data by means of an RR command.  Signal transfer unit 10 may also
request retransmission of t   he last keypad keystroke data by means
of an REJ command.  Each remote viewing unit 2 packages keypad
keystroke data into a message, including the keypad ID and a check
sum for data integrity.  Signal transfer unit 10 gathers keypad
keystroke data by polling each remote viewing unit 2, compiling the
data into one message, which is sent to host computer 8.

      The communication protocol used between host computer 8 and
signal transfer unit 10 is a modified half duplex, bit-oriented, Data
Link Control (DLC) format in a normal response mode.  The...