IBM 1 Series - Page 31

2-20
GA34-0033
i
‘Data strobe’ is activated. The time between ‘address gate return’ and
‘data strobe’ activation, CT2, is 100 nanoseconds, minimum, as seen at
the device interface. The duration of ‘data strobe,’ CT3, as seen at the
device interface, is 200 nanoseconds, minimum. If a parity error is
detected by the channel during a read sequence, ‘data strobe’ is not
activated.
‘Data strobe’ (if it has been activated) and ‘address gate’ are
deactivated simultaneously at the processor channel output. As
denoted by the relationship of CT3 and CT4 in Figure 2-8, ‘data
strobe’ may extend beyond the active envelope of ‘address gate’ by
100 nanoseconds, maximum, but the overlap of ‘data strobe’ and
‘address gate’ is 100 nanoseconds, minimum, as seen at the device
interface.
Upon the deactivation of both ‘address gate’ and ‘data strobe,’ the
device deactivates the ‘condition code in bus’ (and ‘data bus’ on read
sequences), and ‘address gate return.’ The ‘condition code in bus’ (and
‘data bus’ on read sequences) must be deactivated prior to the
deactivation of ‘address gate return.’ The permissible delay, T5, from
the deactivation of both ‘address gate’ and ‘data strobe’ to the
deactivation of ‘address gate return’ is 3 microseconds, maximum. This
delay allows the device attachments to generate additional strobes, to
do additional resetting, and to accomplish interlocked deactivation with
outbound logic. However, unless such functions are necessary, ‘address
gate’ should be deactivated as soon as possible for performance
reasons. All device actions for the command must take place before
deactivating ‘address gate return.’
The total duration of the DPC sequence is timed out by the channel
for error-detection purposes. The total duration is measured as the
time from activation of ‘address bus bit 16’ to the deactivation of
-address gate return.’ If ‘address gate return’ is not deactivated within
the time-out, a machine check occurs and the channel activates the
‘halt or MCHK’ line. Under normal operation, if the device attachment
adheres to the specified times over which it has control, the total
duration of the sequence is within this channel time-out.