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Input/Output Chip Select Doubler

IP.com Disclosure Number: IPCOM000115289D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 57K

Publishing Venue

IBM

Related People

Bennayoun, A: AUTHOR [+3]

Abstract

The problem to solve is the following: In existing adaptor cards for PS/2* or PC, a set I/O accessible by the microprocessor of these adaptors are available. Sometimes, this amount of I/Os are not sufficient for the applications.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 97% of the total text.

Input/Output Chip Select Doubler

      The problem to solve is the following: In existing adaptor
cards for PS/2* or PC, a set I/O accessible by the microprocessor of
these adaptors are available. Sometimes, this amount of I/Os are not
sufficient for the applications.

      Up to now, each I/O is dedicated to one port.  It is to say
that one chip select (CS) from the microprocessor can be connected to
only one chip select of the adapter.  With a few logic, each I/O can
be
doubled. With the same address, the microprocessor can access two
ports
or peripherals.

      This solution can be applied to all the low-speed I/Os which
need more addressability.  Fig. 1 describes the hardware.  Fig. 2
gives
a description of the state machine.
  Software Implementation
  Access to I/O 1 - To access to the I/01, the hardware has to be set
up by 2 consecutive READ or WRITE to the same I/O.  The access is
taken in account at the second operation.
  MOV   DATA,IO_ADD    ;Set the Hardware Logic
  MOV   DATA,IO_ADD    ;Store Data in I/O 1
  Access to I/O 2 - The access to the I/O2 is validated by a NOP
between the 2 accesses to the same I/O. This NOP (a wait in timing)
is decoded to validate I/O2 and the access is validated at the second
operation.
  MOV   DATA,IO_ADD    ;Set the Hardware Logic
  NOP                  ;Select I/O 2
  MOV   DATA,IO_ADD    ;Store Data in I/O 2
  Hardware Timing - Figs. 3 and 4 display access to I/O...