IBM 1 Series - Page 39

2-28
GA34-0033
If the poll is propagated (Figure 2-13):
The device activates the ‘poll propagate’ line to the next device
attachment on the channel. The ‘poll propagate’ output is the image of
‘poll,’ with a delay, T2, of 100 nanoseconds, maximum. The device
must propagate the true DC envelope of the poll without change
except for any internal logic delays less than 100 nanoseconds. Once a
poll is propagated from the device, the device may take no further
action until the activation of the next ‘poll.’ However, if the device
detects a ‘halt or MCHK,’ ‘system reset,’ or ‘power-on reset,’ the ‘poll
propagate’ tag is deactivated at the device output, regardless of the
State of the poll at the device input.
If the poll is captured (Figures 2-11 and 2-12):
The device activates ‘poll return’ or ‘burst return,’ as appropriate, and
deactivates the appropriate ‘request’ line. The ‘request’ line must be
deactivated prior to the activation of ‘poll return’ or ‘burst return.’
‘Poll return’ or ‘burst return’ must be activated at a time, T3, of 100
nanoseconds, maximum, from the activation of ‘poll,’ as seen at the
device interface. The processor channel interface will deactivate the
poll when it sees the active ‘poll return’ tag.
For interrupt-service sequences, the activation of ‘poll return’ causes
the normal service gate sequence to begin without any intervening
DPC sequence. This is necessary to preclude a device reset from
occurring between the poll and service sequences and is necessary for
proper implementation of device reset. The service gate may occur
immediately or may be delayed considerably if another device is
finishing a service sequence (CT3>0).
For cycle-steal operations, service gate may occur immediately or this
tag may be delayed considerably if another device is finishing a
cycle-steal or DPC sequence.
‘Poll’ and ‘poll ID’ are deactivated. The time that ‘poll ID’ remains at
the quiescent value, CT4, is 100 nanoseconds, minimum, as seen at the
device interface. However, ‘poll ID’ cannot be reactivated at the
processor channel output prior to the deactivation of ‘poll’ (or ‘burst
return’) at the processor channel input.
Interrupt or single transfer cycle-steal (‘poll return’)
When ‘poll’ becomes inactive, ‘poll return’ must be deactivated within
a time, T4, of 100 nanoseconds, as seen at the device interface. The
device must not present another ‘request in’ until ‘service gate return’
goes inactive, T5. .