IBM 1 Series - Data Busin; Interrupt Request; Condition Codein; Select Response

Data Bus In
Interrupt Request
Condition Code In
Select Response
6-6
GA34-0033
‘Data bus in’ is an 18-bit inbound bus with 16 bits of data and two 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.
There are 16 inbound ‘interrupt request’ lines from 16 devices (when
configured for 16 device addresses). An external device signals an
interrupt condition by raising its ‘interrupt request’ line. Once this line is
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 ‘strobe’) or (2) the device
receives Device Reset, ‘halt or MCHK,’ ‘system reset,’ or ‘power-on reset.’
‘Condition code in’ is a three-bit binary encoded bus used by an I/O
device to pass status information to the processor during an I/O 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 ‘strobe’ goes active, as
seen at the output of the I/O 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 I/O device to signal
recognition of ‘I/O active’ or ‘interrupt service active.’ This tag also
indicates to the DPC adapter feature that the required inbound data
and/or 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 ‘select response,’ 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,’ as seen at the output of the I/O device.