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that device for use by the other channel if the device is
a dual-channel unit. Execution of this order has no effect
if the device is a sing le-channel unit.
A device is reserved (i.e., it can be used only by the
channels reserving it) whenever an SIO instruction is ad-
dressed to that device. Releasing the device from the
reserved status may be accomplished either by an HIO, a
Release order, or by an
1/0
Reset. The
1/0
Reset releases
al I devices on the control !er, whereas the Release order or
HIO releases only the addressed device. A device may
only be released by the reserving controller.
No data bytes are transferred for the Rel ease order.
SELECT TEST MOOE (X'13')
The Select Test Mode order causes the control !er to make
a service call request for one byte of data. Three bits of
that byte are used to select a test mode in which all sub-
sequent operations wi 11 be performed. Th is order is used
by XDS diagnostic programs.
Bits
01234567
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 1
0 0 0 0 0 0 1 0
00000110
TEST MODE 1
Function
Exit test mode
Enter test mode
Enter test mode
2
Enter test mode 2 - set
test parity error
Test mode
1
al lows the control I er buffer to be fi I led by a
Write order and subsequently read back by a Read order.
Most of the controller's data path is checked without
using the devices.
TEST MODE 2
Test mode
2
allows the controller's data path and control
logic to be tested without using the devices. This mode
tests approximately 90 percent of the controller logic. All
orders may be executed in this mode and device responses
wi 11 be simulated interna I ly. In a Read or Check-Write
order, the data read from the device is simulated by an
incrementing data pattern of
1024
bytes (the first byte
containing the value
224).
TEST PARITY ERROR
While operating in test mode
2,
this condition forces a
data check byte error by changing the first data byte from
224
to
240.
KEY EVENTS
The key events that occur during an
1/0
operation are
described in the following paragraphs. No chronological
i
order of occurrence shduld be assumed from the order of
presentation.
I
STA~T
INPUT/OUTPUT
An
1/0
operation
begi~s
with the execution of an SIO in-
struction by tbe controlll ing system. If
1/0
address recog-
nition exists and the
d~vice
is in the "ready" condition and
available, the controll,ng system sets its
11
1/0
address rec-
ognition" and "SIO ac4epted
11
indicators. The device
advances from the
"rea~y''
to the "busy" condition. It
then requests an order
~yte
from the control Ii ng system and
proceeds with the operqtion defined by the order byte.
I
UNUSAL END CONDITIONS
I
After an order is
receiv~d,
the detection of any of the
fol lowing conditions ca~ses the device to return an
"unusual end" indicatic:)n to the controlling system:
I
1.
Illegal Seek
addre~s.
2.
Incrementing of sttjrage address past end-of-cylinder
number before
cou~t
done s igna I received.
3.
Out-of-range storqge address when Read, Write,
Check-Write, Hea~er Read, or Header Write order
received by contro!ller.
I
4.
Invalid order
code~
5.
Loss of read clock from device while reading headers
or data.
'
6.
Flaw mark while Rtad, Write, Check-Write, or Sense
order is executed. , (The current address is not
incremented.)
'
7.
8.
9.
Device leaving "operational" state while control I er
"busy".
i
!OP halt signaled auring data transmission.
I
Incorrect header
p~rity
check or verification error
while Read, Writer Check-Write, Header Read, or
Sense order being
~xecuted.
(The current address is
not incremented.)'
10.
Receipt of Seek
or~er
when arm in motion.
11.
Occurrence of
Se~k
timeout error when Seek, Read,
Write, Check-Wri~e, Header Read, or Header Write
order received.
1
12.
Attempt to start Hbader Write operation at sector other
than zero.
'
13.
Incorrect length oti Seek order.
CHANN~L
END CONDITIONS
I
"Channel end
11
is reporited to the control I ing system when
any of the following cc:jnditions are detected.
1.
I
Transmission of
4-~yte
address to device during Seek
order. Arm
positi~n
(carriage motion) is not neces-
sarily completed.
Key Events
Q
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