IBM 1 Series Manual page 48

last 'service gate return') to the deactivation of the 'IPL tag' has a
minimum time of 0; the maximum time is device-dependent.
Following the successful completion of IPL and the dropping of the
'IPL' tag, the host IPL device must be prepared to level 0 with its I-bit
on and present an interrupt request to the processor I/O channel. The
device must be available in all other respects. When the interrupt is
accepted, the device presents the device-end interrupt condition code.
©% Initial Sequence to Normal End
Asynchronous I/O activity
Host IPL command —————>
CT2
CT1
System reset
T3
IPL cycle requests and transfers
© Termination and Retry
1. System Reset
IPL
2___»
System reset
2. Hung IPL
Host IPL command
IPL o\
Timings:
T1 > 3 us Legend:
3us<T2 <7 us
T3 >
T4 >
CT1 > 4.8 us
0<CT2 < 500 us
CT3 < 1.8 us
0 CT = channeltimes.
0 T =attachment controlled times
Figure 2-15. Host-initiated IPL sequence timing diagram
Processor I/O Channel 2-37