IBM 1 Series - Other Attachment Considerations

Other Attachment Considerations
Location of Physical and Logical Elements
Printed Circuit Wire Lengths
Signal Clamping
Each device attachment or other circuitry occupying a card socket in a
Series/1 card file must be able to redrive or propagate a poll as part of the
serial polling mechanism. This polling mechanism must be contained on
that part of the device attachment card(s) that plugs into the I/O socket.
This is to ensure that: (1) cabling delays are not encountered (for
example, cabling out to the poll mechanism at the device may cause
incorrect timing sequences to occur depending on cable length and
driving/receiving capability), and (2) powering down a device must not
affect the ability to propagate a poll.
All I/O channel drivers, receivers, and logic necessary to condition
receivers should be on that part of the device attachment card(s) that
plugs into the I/O socket. This includes at least device address comparison
logic, some DPC command logic (for detecting a write sequence), and
service gate capture logic.
IPL logic, to the extent that the attachment should have the ability to hold
the state of the ‘enable IPL cycle steal request and transfers’ pending
device response, should be located on that portion of the attachment that
plugs into and derives power from the I/O socket. Otherwise, this may
preclude the capability of the device to execute a processor-initiated IPL in
auto-IPL mode.
For
attachments to devices that are capable of executing
processor-initiated IPLs, at least that portion of the IPL logic that will
detect and hold the indication that the attached device is to IPL, should
reside on that part of the attachment that plugs into and takes power from
the I/O socket. (See also ‘‘Processor-Initiated IPL Sequence Description”’
and ‘‘Host-Initiated IPL Sequence Description.’’)
Some attachments will service devices and device logic that take power
from a source separate from the power source providing power to the I/O
socket into which the attachment is plugged. Such attachments must be
capable of preventing an I/O check due to a channel time-out if a power
loss occurs on the device or device logic that is separately powered from
the attachment.
Printed circuit wire lengths between I/O channel drivers/receivers and the
connector tabs on the interfacing card should be held to 75 mm (3 in),
maximum. Tag inputs and outputs, and ‘request in’ lines should use shorter
lengths.
All I/O channel circuit modules should have clamping for negative
excursions of the signal input.
Circuit Module Voltage Tolerances
Circuit modules used in device attachments that utilize voltages from IBM
supplies must be capable of operating with +10 percent tolerances from
nominal, as seen at the module pins.
Processor I/O Channel 2-65