Ibm 6643 User Manual download pdf (Page 117)

v

Multiple

messages

occur

when

the

first

error

causes

additional

errors.

Follow

the

suggested

action

of

the

first

error

displayed.

System

resource

conflicts

System

failures

occur

when

there

are

system

resource

conflicts

with

the

following:

v

Interrupt

Request

Queue

(IRQ)

v

Direct

Memory

Access

(DMA)

v

I/O

Address

v

ROM

and

RAM

Addresses.

IRQ

v

Assigns

a

unique

interrupt

request

line

to

every

I/O

device

(line

numbers

range

from

0

to

15).

v

Interrupts

the

processor

to

force

it

to

service

the

request.

v

Handles

interrupts

on

a

priority

basis

(low

numbers

have

the

highest

priority).

v

Queues

interrupt

request.

IRQ

conflicts

occur

when

there

are

multiple

assignments

to

the

same

interrupt

level.

If

there

is

an

IRQ

conflict,

the

system

will

hang.

Use

the

systems

diagnostics

to

check

for

multiple

assignments

to

the

same

interrupt

level

before

replacing

any

hardware

component.

DMA

v

Accesses

the

memory

by

bypassing

the

processor.

This

allows

the

processor

more

time

for

applications

and

programs.

v

Accesses

memory

directly

from

the

serial

and

parallel

ports

on

some

systems.

v

Accesses

memory

directly

from

some

adapters

using

a

DMA

channel.

This

allows

the

adapter

to

operate

faster.

v

Provides

from

4

to

15

DMA

channels.

The

number

varies

depending

on

the

system.

If

multiple

assignments

of

the

same

DMA

channel

occur,

the

system

will

hang.

Use

the

system

diagnostics

to

check

for

multiple

assignments

to

the

same

DMA

channel

before

replacing

any

hardware

components.

I/O

address

A

unique

I/O

address

is

assigned

to

each

system

component.

If

multiple

assignments

of

the

same

I/O

address

occur,

the

system

will

hang.

Use

the

DOS

MEM

command

to

check

for

multiple

assignments

to

the

same

I/O

address

before

replacing

any

hardware

component.

ROM

and

RAM

Addresses

Adapter

cards

with

processors

can

contain

RAM

and

ROM.

If

the

adapter

cards

have

onboard

memory,

then

the

following

are

true.

v

ROM

contains

operating

instructions

for

the

adapter

I/O.

v

RAM

is

used

for

buffering.

Two

adapters

using

the

same

memory

area

will

cause

a

failure.

This

failure

might

appear

as

a

hardware

failure.

Chapter

8.

Related

service

information

109

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