Table of Contents
Advertisement
2. FUNCTIONAL DESCRIPTION
DATA PRESENTATION
Data is transferred from the 1/0 system to the controller on
a one-, two-, or four-byte interface (depending on options
installed) and is transferred between the controller and disk
pack unit serially, bit by bit.
SYSTEM STATES
The initial state of the device depends on its power status.
Complete absence of power removes the device from the
control I ing system (i.e., no address recognition}. If power
is applied to the controller, address recognition occurs
when an 1/0 instruction is issued.
OPERATIONAL STATES
The disk pack system reports the "operational" state if the
1/0 address is recognized and the device is "operational"
as defined below:
l.
Disk speed is within operating limits.
2.
Temperature is within operating limits.
3.
All interlocks are closed.
4.
All power is normal in the controller and disk storage
units.
5.
No "fault" condition exists within a disk storage
unit.
When "operational", an SIO instruction will be accepted if
l.
The addressed controller/device is "ready".
2.
The device is available, that is, not reserved by another
contra
11
er.
3.
No channel interrupts are pending.
The condition of the disk pack system at any given time is
returned to the central processor in response to the 1/0 in-
structions, SIO, HIO, and TIO. Other 1/0 instructions,
TDV and AIO, obtain other specific indications of device
status (see "Status Response").
UNAVAILABLE CONDITION
In the "unavailable" condi1"ion, the device is reserved by
another controller; therefore, it cannot accept an SIO
instruction.
·
READY CONDITION
In the "ready" condition, the controller can accept an SIO
instruction, provided that the addressed device is available
and no channel interrupt is pending. To be "ready" the de-
vice must be "operational" and execution of an order must
not be in progress or pending.
e4sv
CONDITION
In the "busy" condition,! the controller has accepted an SIO
instruction. It wi 11 not IJccept a new order unti I the current
order (or orders} is completed.
I
MODE
The disk pack system is always in the "automatic" mode, as
long as it is in the "operational" state.
TRANSITIONS BETWEEN STATES
Table 2 summarizes the state transitions and conditions re-
quired to cause them.
Table
21.
State Transitions
Present State
N~xt
State
I
Conditions
Ready Automatic
Busy Automatic
Acceptance of
SIO instruction.
I
Busy Automatic
R'ady Automatic
HIO instruction
received, 1/0
reset signal re-
ce ived, or aper-
ation associated
with last order
completed.
DATA TRANSFER
An operation is initiat~d from the controlling system by an
SIO instruction if the fbllowing conditions are satisfied:
I
l.
1/0 address recogpition exists.
2.
Device and controller are in "ready" condition (and
no channel interruipt is pending}.
3.
Device is availabl'e.
If these conditions are !satisfied, the controller enters the
"busy" condition. Th~ controller initiates the transfer of
data to or from the disk pack unit, as specified by the order,
until the required nurmber of bytes have been transferred.
The operation then
ter~inates,
and the device returns to
the "ready automatic" 1state.
Functional Description
3
Advertisement
Table of Contents
