System synchronizes data transfer between two computers by generating data strobe pulses when computers are ready for data transfer. In addition, interface filters noise by sampling

Anderson, T. O.

English

NASA Technical Reports Server

December 1975	 B75-10326 
•
	 NASA TECH BRIEF 
NASA Pasadena Office 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Computer/Computer Interface 
.
A computer/computer interface synchronizes data 
transfer between two computers by generating data 
strobe pulses when the computers are ready for data 
transfer. In addition the interface filters noise by 
sampling. 
The system incorporates eight bidirectional data 
lines connecting the two computers. There are also 
four timing control lines: Two of these are request 
lines which are unidirectional, and the other two are 
bidirectional response and ready lines. The time 
sequence of the control lines is described in the 
following steps; the operation is repeated for each 
linear bit or parallel byte: 
a. The request line is asserted (turned on); 
b. The assertion of the request line is sampled and 
synchronized; 
c. The synchronized request signal allows the asser-
tion of the return response line; 
d. The return resnonse line is s ynchronized and 
allows the assertion of the ready line; 
e. The ready signal is sampled and synchronized and 
can be used to form a data strobe pulse for sam-
pling the received data; 
f. Upon sampling the received data, the ready signal 
can be used to turn off the response line; 
g. The turnoff of the response line allows turnoff of 
the ready line; 
h. The turnoff of the ready line again allows the 
response line to be turned on, which is conditional 
on the request line being on; 
i. At the end of a block transmission the request line 
is turned off simultaneously with the ready line for 
the last character being turned off.
The interface is structured to recognize a signal 
change only when the signal remains in its new state 
for two consecutive clock periods after it has remained 
in its prior state for at least two clock periods. Thus, a 
noise pulse of either polarity of a duration less than 
two clock periods occurring at any time will not be the 
cause of a double data strobe pulse, nor will it 
interrupt the forming of a data pulse or the 
subsequent report level indicating that a data strobe is 
formed. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: TSP75-10326 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Inquiries concerning 
nonexclusive or exclusive license for its commercial 
development should be addressed to: 
Patent Counsel 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Source: Tage 0. Anderson of 
Caltech /JPL 
(NPO-13428) 
Category: 02 (Electronics Systems) 
This document was prepared under the sponsorship of the National
	
Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	
information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19750000326 2020-03-19T20:19:29+00:00Z


Computer/computer interface

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server