IBM Series 1 User Manual page 40

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Seguence Description
Refer to Fiyure 2-9.
executed as follows:
An interrupt service sequence is
1. Service gate is activated. The device detecting the
first leading edge of the service gate activation
following a poll capture is the selected device for the
service sequence. This is called service gate capture.
2. Upon service gate capture, the device activates the
condition code in bus and the data bus and then
activates service gate return. The condition code in
bus and the data bus must be activated prior to service
gate return.
The permissible delay, T2, from service gate to
service gate retuLn as seen at the device interface is
3 microseconds maximum. There is no specific timeout
on this delay_ As with DPC sequences, this delay is
provided for attachment convenience. However, it is
strongly recommended that this delay be held to a
minimum for performance reasons.
3. Data strobe is activated. The time between service
gate return and data strobe, CT1, is 100 nanoseconds
minimum as seen at the device interface. The duration
of data strobe, CT2, is 200 nanoseconds minimum as seen
at the device interface.
4.
Service gate and data strobe are deactivated
simultaneously at the processor channel output. As
denoted
by
the relationship of CT2 dnd CT3 in Pigure
2-9, data strobe may extend beyond the active envelope
of service gate by 100 nanoseconds maximum, hut the
overlap of data strobe and service gate is 100
nanoseconds minimum as seen at the device interface.
5. Upon the deactivation of both service gate and data
strobe, the device deactivates the condition code in
bus. Then the device deactivates service gate return.
The condition code in and data busses must be
deactivated prior to the deactivation of service gate
return as seen at the device interface. The
permissible delay, T4, from deactivation of both
service gate and data strobe, to the deactivation of
service gate return is 3 microseconds maximum as seen
at the device interface. Again this delay is for
attachment convenience, but it is strongly recommended
that the delay be held to a minimum. All device action
for the service must take place prior to dropping
service gate return.
6.
The total duration of the interrupt service sequence is
timed out by the channel for error detection purposes.
The total duration is measured from the activation of
service gate to the deactivation of service gate
return. If, within the timeout, service gate return
Processor I/O Channel 2-25