Browse Prior Art Database

Modem Line Change Detection Reporting Technique

IP.com Disclosure Number: IPCOM000040378D
Original Publication Date: 1987-Nov-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 3 page(s) / 24K

Publishing Venue

IBM

Related People

Morrison, WP: AUTHOR [+4]

Abstract

A method is described which off-loads a main processor from having to sample the state of modem lines, detect valid changes in those lines, and interrupt if any change or lack of a change is detected. Micro-processor technology today is allowing more and more software functions to be performed directly on adapter cards. This has two effects: 1) it off loads the main processor from having to do that function, and 2) it makes the interface between the main processor and the auxiliary micro-processor significantly more complex. The problem arises in how to maximize the function performed by the auxiliary processor with a minimum of data exchange between the two processors. In data communication, where the data exchange is via a modem, there are several control and response lines that the computer must monitor.

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

Modem Line Change Detection Reporting Technique

A method is described which off-loads a main processor from having to sample the state of modem lines, detect valid changes in those lines, and interrupt if any change or lack of a change is detected. Micro-processor technology today is allowing more and more software functions to be performed directly on adapter cards. This has two effects: 1) it off loads the main processor from having to do that function, and 2) it makes the interface between the main processor and the auxiliary micro-processor significantly more complex. The problem arises in how to maximize the function performed by the auxiliary processor with a minimum of data exchange between the two processors. In data communication, where the data exchange is via a modem, there are several control and response lines that the computer must monitor. These lines must follow a sequence as specified in the RS-232-C specification. Any deviation is cause for an error to be reported. Part of the task is to make several different kinds of distinctions in how each line is handled. These are listed as follows: 1) Distinguish between lines that just briefly change state and then change back (glitch detection) and lines that change and stay changed. 2) Lines that change as part of the normal sequence and only need to be reported as errors when the sequence is not followed. 3) Lines that can change state at regular intervals, but only the first change has any significant meaning. 4)

Lines that need to be reported as status every time there is a valid change in its state. The new method allows an I/O processor to off-load a main processor from having to 1) sample the modem lines,
2) determine which lines had valid changes, 3) interpret if the change is an error or just needs to be reported as status, and 4) inform the system with a single status byte when system intervention is required. There are several aspects to the overall implementation, each succeeding aspect builds from the previous to form a hierarchical function that can interpret exactly what is happening with the modem status lines and report only what needs to be reported. This I/O Processor function is the one that does the sampling of the modem status lines and remembers the two previous samples. The sample rate is fixed at 5 milliseconds. With this information it can determine if there was a valid change in any of the lines by comparing the three sample values. Example 1 is a case where noise on the line is detected and rejected. Example 2 indicates a valid state change and would be reported to the next level for interpretation. The alrorithm used for noise detection has the following formula: OUTPUT = ((A XOR C) AND (B XOR C)) The output is a one if the change is a valid change, and the out...