Measurement-computing Isolator488 Manual de usuario descargar pdf (Pagina 31)

Section 3 IEEE 488 Primer

3-10

3.7.14 Parallel Poll Configure (PPC)

This configures devices capable of performing a

Parallel

Poll

as to

which data bit they are to assert in response to a

Parallel

Poll

. ($05)

3.7.15 Parallel Poll Unconfigure (PPU)

This disables all devices from responding to a

Parallel Poll

. ($15)

3.8 MORE ON SERVICE REQUESTS

Most of the commands covered, both uniline and multiline, are the

responsibility of the

Active Controller

to send and the bus devices to

recognize. Most of these happen routinely by the interface and are totally

transparent to the system programmer. Other commands are used directly

by the user to provide optimum system control. Of the uniline commands,

SRQ

is very important to the test system and the software designer has easy

access to this line by most devices. Service Request is the method by which

a bus device can signal to the

Controller

that an event has occurred. It is

similar to an interrupt in a microprocessor based system.

Most intelligent bus peripherals have the ability to assert

SRQ

. A

DMM might assert it when its measurement is complete, if its input is

overloaded or for any of an assortment of reasons. A power supply might

SRQ

if its output has current limited. This is a powerful bus feature that

removes the burden from the

System Controller

to periodically inquire,

"Are you done yet?". Instead, the

Controller

says, "Do what I told you to

do and let me know when you're done" or "Tell me when something is

wrong."

Since

SRQ

is a single line command, there is no way for the

Controller

to determine which device requested the service without

additional information. This information is provided by the multiline

commands for

Serial Poll

and

Parallel Poll

1 2 ... 26 27 28 29 30 31 32 33 34

Comentarios a estos manuales

Sin comentarios

Measurement-computing Isolator488 Manual de usuario Pagina 31

Comentarios a estos manuales

Relacionado con productos y manuales para Hardware Measurement-computing Isolator488