IBM 1 Series - Functional Description of I;O Channel Signal Lines

The I/O channel signal lines are distributed internally via the processor
backpanel board to each I/O attachment card socket. Distribution of the
channel signal lines can be continued by connecting cables or a channel
repower feature from a processor I/O socket (usually the A-socket) to an
adjacent I/O expansion unit, as the particular processor or configuration
requires. Refer to the IBM Series/1 Configurator, GA34-0042, for details
about the requirements for the use of the repower feature.
IBM I/O attachment cards plug directly into the backpanel sockets.
External I/O devices are connected to the attachment cards via top-card
connectors.
Two features are available for connecting non-IBM devices directly to the
channel: the channel socket adapter feature and the channel repower
feature.
e Channel socket adapter feature—this feature consists of an IBM
printed circuit card that plugs into the backpanel of the processor unit
or I/O expansion unit. An industry-standard connector on the top
edge of the IBM printed circuit card accepts the user’s I/O adapter
card. For further information, see ‘““Socket Adapter Feature’’ in this
chapter.
e Channel repower feature—this feature is a logic card that repowers
and isolates the channel signal lines. This card can be installed in any
I/O socket, as the last series element on the channel, to allow
connection of additional I/O adapters or controllers. For further
information, see ‘‘Channel Repower Feature” in this chapter.
If the user connects directly to the channel at the backpanel sockets
instead of through one of the available features, the unit load, the power,
and the physical requirements must be considered. These and other
requirements are discussed in subsequent sections of this chapter.
CAUTION: To achieve adequate results, good design practices—both
electrical and mechanical—must be adhered to. IBM bears NO
RESPONSIBILITY for customer logic or hardware.
Functional Description of I/O Channel Signal Lines
2-2 GA34-0033
The I/O channel consists of 81 signal lines divided into two physical
groups: the service group and the poll group. Each group can operate
concurrently and asynchronously with the other group; however, the
initiation of sequences on the channel is interdependent.
The service group supports:
e Data and control information transfers
e IPL initiation
e Reset functions
The poll group supports:
e Cycle-steal requests from the devices
e« Interrupt requests from the devices
e Acknowlegement of both types of requests