IBM Series 1 User Manual page 188

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Data bus in is an 18-bit inbound bus with 16 bits of data
and 2 parity bits, odd parity by byte. This bus is used to
transfer data and status information from the devices to the
processor and is activated by selected devices during Read
Data, Read status, or an interrupt service active sequence.
When the parity option is not selected, the device generates
only 16 bits of data.
Interr~£! Reg~!2
The interrupt requests are 16 inbound lines from 16 devices
(when configured for 16 device addresses). An external
device signals an interrupt condition by raising its
interrupt request line. Once raised, a device must keep its
request active until (1) it is serviced (the interrupting
device activates the select response tag during an interrupt
service active sequence and receives the strob~ or
(2)
the
device receives Halt or ~CHK, a device reset, system reset,
or power-on reset.
Condition code in is a 3-bit binary encoded bus used by an
IIO
dev ice to pass sta tus information to t.he processor
during an 1/0 active sequence or an interrupt service active
sequence.
The condition code in bus is activated with the rise of
the select response tag and is maintained active at least
until the strobe goes active as seen at the output of the
1/0
device. Once a value is activated on the condition code
in bus, it is not changed.
Select response is an inbound tag sent
by an
1/0
device to
signal recognition of
I/O
active or interrupt service
active. The tag also indicates to the DPe adapter feature
that the required inbound data andlor control information
for the transfer has been placed on the interface. Any data
or information must be activated on the interface no later
than the rise of this tag, as seen at the output of the I/O
device. This tag
may fall no sooner than the fall of I/O
active or interrupt service active. This is as seen at the
output of the
1/0
device.
Customer DPC Adapter 6-7