IBM 3745 Series, Hardware Maintenance Reference

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Interrupt Requests
The CA generates two major classes of interrupt: CA level 1 and CA level 3 inter-
rupt requests.
Level 1 Interrupt Request
This request is associated with hardware detection of errors in the CA. When an
error condition is detected in the CA, a bit is set in the CA level 1 interrupt check bit
register X'0D'.
These errors raise a level 1 interrupt request to the CCU by activating IOC bus byte
0, bit 5 (if register X'09' bit 0.4, 'interrupt request disabled', is OFF).
Level 3 Interrupt Request
A CA raises a level 3 interrupt request to the CCU by activating IOC bus byte 1, bit
0 when the I/O is not active (if register X'09' bit 0.4, 'interrupt request disabled', is
OFF). There are two types of level 3 interrupt request:
1. CA initial selection request:
Ÿ An initial selection sequence occurs if buffer chaining is not set
Ÿ
An initial selection sequence occurs for commands other than Read, TIO or
NO-OP when buffer chaining outbound is set
Ÿ An initial selection sequence occurs for commands other than Write, Write-
Break, TIO ot NO-OP when buffer chaining inbound is set
Ÿ NSC status cleared if buffer chaining is not set
Ÿ A system reset sequence occurs
Ÿ
ESC TIO status cleared
Ÿ Selective reset
Ÿ Interface disconnect
Ÿ Channel bus out check
2. Data/status transfer request:
Ÿ
End of an inbound data transfer if buffer chaining is not set
Ÿ End of an outbound data transfer if buffer chaining is not set
Ÿ End of a status transfer if buffer chaining is not set
Ÿ End of the last inbound data transfer if buffer chaining is set (for example
end of PIU)
Ÿ
End of the last outbound data transfer if buffer chaining is set (for example
end of PIU chain)
Ÿ Suppress out monitor interrupt.
Ÿ A program requested interrupt occurs.
Ÿ Any CA level 1 check occurs when the adapter is in a data/status transfer
sequence.
Ÿ
A data streaming time out interrupt occurs
Ÿ A channel bus out check
Ÿ A selective reset or an interface disconnect when the CA is in
data/status/IO error alert sequence.
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IBM 3745 Models 130, 150, 160, 170, and 17A: Hardware Maintenance Reference