Parallel Poll - Brainboxes PS-307 User Manual

IEEE 488 Introduction
The serial poll response of each device is held in bytes 28-
30 of the IEEE control status string when that device is
addressed as the current device. The serial poll response contains
data concerning the service request.
If bit 6 (value 64) of the devices serial poll response is set
then that device was requesting service, the other bits in the
response byte will contain a code indicating the nature of the
service requested.
Conversely if bit 6 (value 64) of the serial poll response is
not set then this device did not request service.
Several devices can assert SRQ true at one time so it is
good practise to check that SRQ has returned false after the
Serial Poll routine to ensure that all devices that have requested
service are monitored.
In general, many devices have the ability to assert service
request and respond to serial polls.

Parallel Poll.

___________
The Parallel Poll function allows the IEEE controller to
periodically check selected bus devices to see if they require
some special service.
The Parallel Poll makes good use of the controller's time
since it can quickly check the state of 8 or more devices with
one command. Unlike the Serial Poll which is conducted after a
device requests service, the Parallel Poll routine is initiated by
the controller. It allows a whole group of devices to
simultaneously return a status bit on the data lines. The data
line, and the sense of each devices response is determined by the
controller when it issues a CONFIGURE command or PPC,
parallel poll configure. Devices power up in the PPU state and
cannot respond to the Parallel Poll until after they have been
configured.
The Controller knows which device responds on which
data line because it has previously assigned those lines to each
Chapter 2
PSI BOX Reference
Page 21