Browse Prior Art Database

Programmable Arbitration Interface Permits to Configure Pins Two Ways

IP.com Disclosure Number: IPCOM000103616D
Original Publication Date: 1993-Jan-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 3 page(s) / 120K

Publishing Venue

IBM

Related People

Clarke Jr, GL: AUTHOR [+4]

Abstract

This article describes a technique for use in a computer system that allows connecting bidirectional open collector/drain interface pins of an arbitration interface directly or via transistor to transistor logic (TTL) buffers to a MICRO CHANNEL*.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Programmable Arbitration Interface Permits to Configure Pins Two Ways

       This article describes a technique for use in a computer
system that allows connecting bidirectional open collector/drain
interface pins of an arbitration interface directly or via transistor
to transistor logic (TTL) buffers to a MICRO CHANNEL*.

      As a general rule complementary metal-oxide semi-conductor
(CMOS) devices are not interfaced directly to the MICRO CHANNEL.  The
reason is susceptibility of CMOS technology to latch-up.  If,
however, the transmission lines of the MICRO CHANNEL are designed so
that reflections are not exceeding latch-up conditions (this is more
likely to be accomplished on a system with a small number of slots)
and hot plugging can be assumed not to occur, CMOS devices unbuffered
can be connected to the MICRO CHANNEL.

      An I/O controller module provides dual capability for the
arbitration interface, consisting of inputs, outputs and open
collector/drain pins, where the open collector nomenclature is used
for bipolar technology and open drain for metal-oxide semi-conductor
(MOS) technology.  Input and output pins require no modification.
The bidirectional open collector/drain pins, however, require special
consideration in this application.  These signals are Preempt and Arb
0 through 3.  Due to the nature of the interface, these signals must
be designed in open drain configuration when directly driving the
MICRO CHANNEL or buffered by open collector TTL devices.

      In the I/O controller module two configurations are supported.
If these signals are to be buffered before interfacing to the MICRO
CHANNEL, separate pins are used for each of the Preempt and
Arbitration level 0 through 3 inputs and outputs.  Bidirectional pins
are used when the interface is connected unbuffered to the MICRO
CHANNEL.  A signal called 힯5 SLOTS determines the configuration.
The buffered interface is enabled when this signal is high (16 slots
in the channel); otherwise, it is low (i.e., 5 slots in the channel).
The pin interface design of -PREEMPT is similar to that of Đ 0
through Đ 3.  Therefore, only -PREEMPT is described.

      Fig. 1 shows a direct interface to MICRO CHANNEL.  In this
configura...