Input/Output Operati Ons; External Dio Interface; Multiplexor Input/Output Processor (Miop); Device Controllers - Xerox 560 Reference Manual

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4. INPUT jOUTPUT OPERATIONS
To accommodate the variety and number of I/o devi ces
which may be required for scientific and commercial appli-
cations, a Xerox 560 computer system may include the fol-
lowing:
External Direct Input/Output (DIO) interface,
Multiplexor Input/Output Processors (MIOPs), and Rotating
Memory Processors (RMPs).
EXTERNAL DlO INTERFACE
An external DIO interface permits standard and specially
designed I/O devices to perform I/O operations (normally
in a real-time environment) that are controlled directly by
the basic processor (BP). Appropriate control signals and
up to one word {32 bi ts} of data may be exchanged between
the BP and an addressed I/O device for each READ DIRECT
or WRITE DIRECT instruction executed by the BP.
During a WRITE DIRECT instruction (Mode
2
through F),
the BP holds the control and data-lines stable until an
acknowledgment signal is received from the addressed I/O
device.
During a READ DIRECT instruction (Mode 2
through F), the BP holds the control lines stable until the
addressed I/o device furnishes the data accompanied with
an acknowledgment signa/.
Any delay encountered in
receiving the acknowledgment signal, for either READ
DIRECT or WRITE DIRECT instructions, does not have an
adverse effect upon I/O operations being performed by
the MIOP or RMP systems.
Refer to Xerox publication 90 09 73 {Interface Design
Manual} for further detai Is pertaining to the external DIO
interface.
Also, refer to appropriate peripheral reference
manuals for details on control and data signals.
MULTIPLEXOR INPUT/OUTPUT PROCESSOR (MIOP)
An MIOP permits standard and commercially available I/O
devices (e. g., card readers, card punches, magnetic tape
units, etc.) to be controlled primari Iy by individual I/O
subchannels within the MIOP and associated device con-
trollers. Depending upon the number of I/o subchannels
assigned (maximum of 16, as described under
II
Device Con-
trollers"), an equivalent number of I/O operations may be
performed si mu
I
taneously.
DEVICE CONTROLLERS
All I/O devices associated with an MIOP are connected
via an appropriate device controller.
Depending upon the
number and type of I/o devices to be connected, one or
142
Input/Output Operati ons
more of the following types of device controllers may be
connected to
an
MIOP:
1.
Single-unit device controller {internal or external}.
2.
Multi-unit device controller {internal or external}."
3.
Unit-record controller {internal or external}.
Generally, an internal device controller is physically con-
nected via the internal I/o interface.
An external device controller is located remotely to the
MIOP and may require one or more separate chassis to ac-
commodate it.
A single-unit device controller {internal or external} is
specifically designed to control only one I/o device,
usually a unit-record device such as a card reader, a card
punch, or a line printer. Characteristics of a single-unit
device controller are dependent upon the device controlled.
(Refer to an appropriate peripheral reference manual for
further information. )
A multi -unit device controller (internal or external) is
specially designed to control more than one I/o device,
where all the I/O devices are of the same type {e. g.,
magnetic tape units or RADs}.
However, only one I/o
device at a time may be actively involved in a data trans-
fer operation. Characteristics of a multi-unit device con-
troller are dependent upon the I/O devices controlled. For
example, a multi -unit device controller for magnetic tape
units may control up to eight units. (Refer to an appropriate
peripheral reference manual for further information.)
Unit-record controllers {internal or external} are designed
to control up to eight unit record type of I/O devi ces (e. g. ,
card readers; card PlJnches; line printers).
AI!
I/o
de-
vices attached to a unit-record controller need not be of
the same type. All I/o devices attached to a unit-record
controller may perform separate I/O operations, including
data transfers, si mu I taneously.
The number of device controllers, as well as the number of
I/O devices, that may be connected to an MIOP is depen-
dent upon the following considerations:
1.
The maximum number of I/O subchannels within an
MIOP is 16.
2.
Each single-unit device controller {internal or external}
requires one I/o subchannel.
3.
Each multi-unit device controller (internal or external)
requires one of the first eight subchannels within
the MIOP.

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