IOtech Personal488, Руководство пользователя

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Personal488 for Windows 95/98/Me/NT/2000
04-10-01
API Reference 6-40
PPoll
Syntax INT WINAPI PPoll(DevHandleT devHandle);
devHandle refers to either an interface or an external device. If devHandle refers to an
external device, then the PPoll command acts on the hardware interface to which the
external device is attached.
Returns -1 if error
otherwise, a number in the range 0 to 255
Bus States
ATN
•
EOI, *EOI
Example errorcode = PPoll(ieee);
See Also
PPollConfig, PPollUnconfig, PPollDisable, SPoll
The
PPoll
(Parallel Poll) command is used to request status information from many bus devices
simultaneously. If a device requires service then it responds to a Parallel Poll by asserting one of the eight
IEEE 488 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 (
SPoll
) 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
responds 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
PPoll
capabilities are supported.