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Alto Hardware Manual
A[15]
0-1
Section 6: Disk and Controller
45
o
normally.
1 if cylinder 0 is to be addressed via a hardware
"restore" operation.
A disk command word C contains the following fields:
FIELD
RANGE
C[0-7]
110B
C[8-9]
0-3
C[1O-11]
0-3
C[12-13]
0-3
C[14]
0-1
C[15]
0-1
A disk status word S has the following fields:
FIELD
VALUES
S[0-3]
0-13B
S[4-7]
17B
S[8]
0-1
S[9]
0-1
S[10]
0-1
S[11]
0-1
S[12]
0-1
S[13]
0-1
S[14-15]
0-3
SIGNIFICANCE
Checked to verify that this is a valid disk command.
o
if Header block to be read.
1 if Header block to be checked.
2 or 3 if Header block to be written.
o
if Label block to be read.
1 if Label block to be checked.
2 or 3 if Label block to be written.
o
if Data block to be read.
1 if Data block to be checked.
2 or 3 if Data block to be written.
o
normally.
1 if the command is to terminate immediately after
the correct cylinder position is reached (before any
data is transferred).
xOR'ed with A[14] to yield hardware disk number.
SIGNIFICANCE
Current sector number.
One can tell whether status has been stored by
setting this field initially to 0 and then checking for
non-zero.
1 means seek failed, possibly due to illegal cylinder
address.
1 means seek in progress.
1 means disk unit not ready.
1 means data or sector processing was late during the
last sector.
Data and current sector number
unreliable.
1 means disk interface was not transferring data last
sector.
1 means checksum error. Command allowed to
proceed.
o
means command completed correctly.
1 means hardware error (see S[8-11]) or sector
overflow.
2 means check error. Command terminated instantly.
3 means disk command specified illegal sector.
Several clever programming tricks have been suggested to drive the disk controller.
For an initial
program load, KBLK should be set to point to a. disk command block representing a read into location
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