Measurement-computing Digital HS Manuel d'utilisateur télécharger pdf (Page 44)

4.4.2 Interface Clear (IFC)

The

IFC

line is used only by the

System Controller

. It is used to place all bus

devices in a known state. Although device configurations vary, the

IFC

command

usually places the devices in the Talk and Listen Idle states (neither

Active Talker

nor

Active Listener

4.4.3 Remote Enable (REN)

When the

System

Controller

sends the

REN

command, bus devices will respond to

remote operation. Generally, the

REN

command should be issued before any bus

programming is attempted. Only the

System

Controller

has control of the

Remote

Enable

line.

4.4.4 End or Identify (EOI)

The

EOI

line is used to signal the last byte of a multibyte data transfer. The device

that is sending the data asserts

EOI

during the transfer of the last data byte. The

EOI

signal is not always necessary as the end of the data may be indicated by some special

character such as carriage return.

The

Active

Controller

also uses

EOI

to perform a

Parallel

Poll

by simultaneously

asserting

EOI

and

ATN

4.4.5 Service Request (SRQ)

When a device desires the immediate attention of the

Active

Controller

it asserts

SRQ

. It is then the Controller's responsibility to determine which device requested

service. This is accomplished with a

Serial Poll

or a

Parallel Poll

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Measurement-computing Digital HS Manuel d'utilisateur Page 44

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