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STATUS RESPONSE
The controller reports the status in response to I/o instruc-
tions and device orders.
The Overflow and Carry indica-
tors, Condition Codes, and the Device Status Byte are set
as the result of an I/O instruction.
(Explanations of the
I/O instructions appear in the appl icable Xerox computer
reference manua I.) The Operational Status Byte, however,
is set as the result of a device order.
addressed controller and device.
(CC3 may also be set bl
an I/o instruction.
'Iv11en set, it means either that
t~.~
status returned in the registers is not reliable or that the
status has not been returned.
When reset (zero), it means
that the status information is rei iable.
However, CC3 is
set by the lOP, not by the controller.)
Table 7 lists the
possible settings for CCl and CC2 for each
VO
instruction
and the significance of each setting.
OVERflOW AND CARRY INDICATORS
DEVICE STATUS BYTE
Overflow and Carry indicators apply to the Xerox 530 and
Sigma 3 computers only. These indicators report the gen-
eral status of the addressed controller and device. Table 7
lists the possible settings of the Overflow and Carry indica-
tors for each I/O instruction and the significance of each
setting.
The Device Status Byte is returned in response
tr~
the execu-
tion of each I/O instruction.
Tables 8, 9, aile-
iO
list the
possible settings of the Device Status Byte for eac;)
Vo
in-
struction, and the significance of each setting.
OPERATIONAL STATUS BYTE
CONDlnON CODES
Condition Codes apply to the Xerox Sigma
5/6/1
/8 com-
puters only.
CCl and CC2 report the general status of the
The controller generates the order- in status (Operational
Status Byte) at the conclusion of each I/o operation.
The
significance of the bits is
pr~sented
in Table 11.
Table 7. Overflow and Carry Indicators and Condition Codes
Overflow
f
Carryt
Indicator
Indicator
I/O Instruction
or CCl
or CC2
Significance
!
I
SIO
0
0
I/O address recognized and SIO accepted (the controller has entered
the busy condition).
X
'*fO'+1'
0
1
I/o address recognized but SIO not accepted (the controller was
already busy or a device interrupt is pending).
1
0
Selector lOP busy.
tt
1
1
I/O address not recognized.
HIO
0
0
I/o address recognized and the controller was not busy when the halt
occurred.
X '10
'tl'
0
1
I/O address recognized and the controller was busy when the halt
occurred.
1
0
Invalid code.
1
1
I/o address not recognized.
TIO
0
0
I/O address recognized and SIO can currently be accepted (the
controller is in the ready condition with no device interrupt pending).
X'AO'fl
0
1
I/O address recognized but SIO cannot currently be accepted.
1
0
Se I ector lOP busy.
tt
I
1
1
I/O address not recognized.
Status Response
17
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