IBM Series 1 User Manual page 46

o
c
o
Poll Sequence DescriEtiQ~
Refer to Figures 2-11, 2-12 and 2-13. The poll sequences
with poll return or burst return are executed as follows:
1.
When the device detects an interrupting condition, it
activates the appropriate bit of the request in bus as
determined by the level field and I-bit of the Prepare
command. The device may activate an interrupt request
on the interface only while its I-bit (device mask) is
on, or equal to a logical 1.
Once the bit of the request in bus is activated,
the bit must remain active until the device has
captured a poll, executed a prepare command setting the
device I-bit off, or received: a device reset, Halt or
MCHK, system reset, or power on reset. If an I/O
device has an interrupt request active and executes a
device reset or prepare command, the device, as
appropriate, drops its request or alters its requested
level prior to the deactivation of data strobe as seen
at the device interface.
When the device requires an access to storage, it
activates the cycle steal request in line. Once the
cycle steal request in has been activated, the line
must remain active until the device has captured a
poll, or received a Halt or
MCHK,
system reset, or
power on reset. If the device has already activated a
cycle steal request on the interface and detects a
device directed reset, the device must complete the
servicing for that request. This servicing is a dummy
transfer and is to be an output transfer (read from
storage). In the case of burst mode, the dummy
transfer must appear as the last transfer of the burst
mode. Because the channel is unaware that these are
dumay transfers, no device-held parameters are to be
updated nor are any status conditions to be recorded or
reported by the device.
2. Poll
1D
is activated, either as a result of the
particular device's request, or from other requests
previously presented to the channel. Therefore, poll
ID and a subsequent poll can occur completely
asynchronous to the device's request. When the device
detects activation of the pollIO bits relevant to the
type of requests the device has activated (interrupt or
cycle steal), the device must not allow its state of
request to further influence the decision to capture or
propagate the poll tag.
1
time, T1, (measured at the
device interface) of 100 nanoseconds after the
activation of poll ID and the device request becoming
active is the latest time in which a device should
allow a further request to influence the decision to
capture or propagate.
3. Poll is activated. The time, CT1, from the activation
of the poll identifier to the activation of poll is 180
nanoseconds minimum. Poll is held valid until the
Processor I/O Channel 2-31