IBM Series 1 User Manual page 216

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TNL: GN34-0368 to GA34-0033-0 (February 4,1977)
Refer to Fiqure 2-14. The processor initiated IPL sequence
is executed as follows:
1 •
The initiate IPL line is activated at the processor
channel output, along with status bus bit
a
or 1, as a
result of pressing the load key. status bus bit 0 and
1 reflect the position of the
IPL
source switch,
primary or alternate, at the time the load key was
pressed. The first system reset in the sequence is
also activated
at this
time. Initiate
IPL
and
the
status bus are held valid until the activation of the
1PL tag at the processor channel input after the first
sytem reset is deactivated.
On
the activation of the logical
'AND' of
initiate
IPL and system reset, the device must dc reset the
IPL
tag within 200
ns,
T1, as seen at the device interface.
On activation of the first system reset, the device
executes all other system reset functions. Because of
possible skew, system reset may lag initiate IPL and
the status bus at the device interface. Therefore, the
IPL
tag may temporarily become active at the device
interface prior to
the
first system reset. However,
the processor channel ignores the IPL tag during the
initial part of the sequence and does not examine it
until the first system reset has been activated.
In no case should the device use the leading-edge
transition of the first system reset. This is because
the first system reset could also lead the initiate 1PL
and status bus at the device interface.
2. The first system reset is deactivated after a time,
CT1,
of 4.8 microseconds minimum at the device
interface. The IPL source device then activates the
1PL tag. The time, T2, from the deactivation of the
first system reset to the activation of the 1PL tag
must be g~eater than zero as seen at the device
interface, but the maximum time is device dependent.
This maximum time should be kept within reasonable
limits, and generally this time should only depend upon
electronic rather than mechanical delays.
3. As a result of 1PL going active, initiate IPL is
deactivated. The status bus is not valid for the
primary/alternate selection portion of the 1PL sequence
after the time when initiate IPL is deactivated.
Processor I/O Channel
2-37