Measurement-computing Micro 488/EX rev.2.1 Manuel d'utilisateur télécharger pdf (Page 128)

Section 5 Command Descriptions

5.58

PPOLL

The Parallel Poll command,

PPOLL,

is used to request status information from

many bus devices simultaneously. If a device requires service then it will respond to a

Parallel Poll by asserting one of the eight IEEE bus data lines (DIO1 through DIO8,

with DIO1 being the least significant). In this manner, up to eight devices may

simultaneously be polled by the controller. More than one device can share any

particular DIO line. In this case it is necessary to perform further Serial Polling to

determine which device actually requires service.

Parallel polling is often used upon detection of a Service Request (SRQ), though

it may also be performed periodically by the controller. In either case,

PPOLL

will

respond with a number from 0 to 255 corresponding to the eight binary DIO lines.

Not every device supports parallel polling. Refer to the manufacturer's

documentation for each bus device to determine if Parallel Poll capabilities are

supported.

SYNTAX PPOLL

RESPONSE Number in the range of 0 to 255

MODE CA

BUS STATES ATN•EOI,<parallel poll response>, *EOI

EXAMPLE

PRINT#1"PPOLL"

Conduct a Parallel Poll

INPUT#1,PPSTAT

Receive the

PPOLL

status

PRINT PPSTAT

1 2 ... 123 124 125 126 127 128 129 130 131 132 133 ... 217 218

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Measurement-computing Micro 488/EX rev.2.1 Manuel d'utilisateur Page 128