Browse Prior Art Database

Enhanced Internal Modem for Computers

IP.com Disclosure Number: IPCOM000111296D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 145K

Publishing Venue

IBM

Related People

Angwin, AJ: AUTHOR [+2]

Abstract

Described is an interface between computers with internal modems that is capable of higher throughput than conventional serial interfaces, yet can maintain compatibility with older formats, if needed. The traditional UART enhanced-access chip is bypassed or can be switched back for compatible access. It permits new sophisticated and adaptive transmission protocols to be considered to ensure the maximum throughput of data via media of variable quality, e.g., radio communications.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 43% of the total text.

Enhanced Internal Modem for Computers

      Described is an interface between computers with internal
modems that is capable of higher throughput than conventional serial
interfaces, yet can maintain compatibility with older formats, if
needed.  The traditional UART enhanced-access chip is bypassed or can
be switched back for compatible access.  It permits new sophisticated
and adaptive transmission protocols to be considered to ensure the
maximum throughput of data via media of variable quality, e.g., radio
communications.

      Modems have traditionally been attached to a computer via an
RS232 interface using the CCITT V.24 protocol covering serial data,
Ring Indication, Ready To Send, Clear To Send, etc.  This is a simple
effective interface where the Modem is external to the computer, a
situation which is common today.  The serial interface provided both
COMMAND mode interface to the modem, i.e., setting up the Modem via
commands or direct programming of the modem's 'S' registers, or DATA
mode interface, i.e., the transmitted data.  Personal Computers (PCs)
have options now for internal modems where the modem contains an
interface which is one of two types:

PC bus interface which is the interface of a Serial Communications
port
     controller, identical in every way to the serial controller used
to
     provide external serial communications via such devices as
modems.

PC Comm Port which is the serial interface side of a dedicated serial
     communications device within a computer whose serial interface
is
     dedicated to some internal device such as a modem.  The logic
levels
     are often not converted into the conventional RS232 interface
     levels, remaining at the normal logic 1 and 0 levels for the
host
     computer system.

      In both cases the interface is usually compatible to the 8250
serial communications controller, and is usually addressed at one of
the allocated addresses for secondary serial communications, namely,
2F8hex or 3E8hex, the primary PC serial port being at 3f8hex.  While
modem line performance, i.e., the data transmission rate, is low,
either of these two interfaces is acceptable.  Both approaches
require the established protocols to ensure the modem is aware of the
nature of the information being communicated to it, i.e., whether
COMMAND or DATA.  This normally involves the procedure of issuing an
ESCAPE sequence to break the transmission of data and then resuming
after the host computer has concluded sending COMMANDS to the modem
and receiving the necessary responses, all of this communication
being done at the serial data rate established between host and
modem.  In the case of the PC Comm port interface to an internal
modem the performance expected is little better than the original
external modem scenario, any improvement being limited to the benefit
accrued by the removal of the transmit and receive level converting
processes required for the R...