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Nibble-Wide Bidirectional Personal Computer Parallel Port Communication Interface

IP.com Disclosure Number: IPCOM000039917D
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Moosavi, SR: AUTHOR [+2]

Abstract

A technique is described whereby nibble-wide bidirectional communica- tions is provided to enable point-to-point communication between two IBM personal computers (PCs) for message and file transfers. No modifications are made to the existing PC parallel communication circuit cards. Four control lines going out and four control lines going in are provided as an interface to two PCs connected together by means of a cable, enabling the two interface cards to exchange nibble-wide (4 bits) data. The hardware interface along with the pseudo-code described herein, provide a method of implementing a disk operating system (DOS) extension which will copy files and facilitate the field upgrade of PCs with different disk drive formats, such as a 5.25" PC drive being able to exchange data with a 3.5" PC drive.

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Nibble-Wide Bidirectional Personal Computer Parallel Port Communication Interface

A technique is described whereby nibble-wide bidirectional communica- tions is provided to enable point-to-point communication between two IBM personal computers (PCs) for message and file transfers. No modifications are made to the existing PC parallel communication circuit cards. Four control lines going out and four control lines going in are provided as an interface to two PCs connected together by means of a cable, enabling the two interface cards to exchange nibble-wide (4 bits) data. The hardware interface along with the pseudo-code described herein, provide a method of implementing a disk operating system (DOS) extension which will copy files and facilitate the field upgrade of PCs with different disk drive formats, such as a 5.25" PC drive being able to exchange data with a 3.5" PC drive. Using a ten-wire cable, pins 2 and 15 are designated as the control lines and are connected so that pin 2 of one PC connects to pin 15 of the other PC. For nibble data line communications, pin 1 is connected to pin 13, pin 14 is connected to pin 12, pin 16 is connected to pin 10, and pin 17 is connected to pin 11, pin 13 is connected to pin 1, pin 12 is connected to pin 14, pin 10 is connected to pin 16 and pin 11 is connected to pin 17 or the other PC. The following pseudo code is provided to illustrate the software implementation of the nibble-wide bidirectional communications feature: Transmission procedures: Send_message

Place message length counter at head of data buffer

Set message buffer pointers and message length counter

Place 1st byte in 8-bit register

Do until all bytes sent: (Note: In this protocol, header=

message length)

Call Send_Byte

If successful - Continue; Else - Report & Quit

Increment pointers; Decrement counter

Place next byte in 8-bit register

EndDo

End Send_Byte

Save message byte

Zero-out MSN in message byte (sending LSN lst)

Set FLAG indicating first nibble

Continue Send Operation

Send message byte OUT parallel data port

Set Strobe='HI' (Makes ACK='HI' on receiver, indicating byte was

sent)

Wait for ACK='HI' (indicates acknowledgement of byte sent)

If no Time-out - Continue; Else - report error & quit

Set strobe='LO' (Makes ACK...