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Doubleword
Doubleword
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•
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Word (even address)
Word (odd address)
Word (even address)
Word (odd address)
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Halfword 0
Halfword 1
Halfword 0
Halfword 1
Halfword 0
Hal fword 1
Halfword 0
Halfword 1
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: Byte 01 Byte 1 Byte 21 Byte 3 Byte 0 1 Byte 1 Byte 2/ Byte 3 Byte 0 / Byte 1 Byte 2\ Byte 3 Byte 0
1
Byte 1 Byte 2[ Byte 3!
Figure 2. Information Boundaries
Table 1.
SIGMA 6 Dedicated Memory Locations
Location
Decimal
Hexadecimal
Function
0
0
Addresses of general registers
15
F
16
10
Reserved for future use
31
1F
32
20
Cpu/Iop communication
33
21
34
22
Program stored by LOAD
switch on the processor panel
41
29
42
2A
First record read from peri-
phera
device during a load
63
3F
operation
64
40
Traps (see Table 3)
79
4F
80
50
Override interrupt levels t
87
57
88
58
Counter interrupt level/
91
5B
92
5C
Input/output interrupt level/
93
5D
94
5E
Reserved for future use
t
95
5F
96
60
External interrupt level/
319
13F
tSee Table 2
COMPUTER MODES
The SIGMA 6 computer operates in either the master mode
or the slave mode. The mode of operation is determined
by the state of the master/slave mode control bit in the
arithmetic and control unit.
MASTER MODE
The master mode is the basic operating mode of the
computer. In this mode, all SIGMA 6 instructions are
permissible. It is assumed that there is a resident execu-
tive program (operating in the master mode) that controls
and supports the other programs operating in the master
or slave mode.
SLAVE MODE
The slave mode is the problelT)-solving mode of the com-
puter.
In this mode, "privileged" instructions are pro-
hibited.
Privileged instructions are those relating to input/
output and to changes in the basic control state of the com-
puter. All privileged instructions are performed in the
master mode only. Any attempt by a program to execute a
privileged instruction while the computer is in the slave
mode results in a return of control to the resident execu-
tive program.
The master/slave mode control bit can be changed only
when the computer is in the master mode; thus, a slave pro-
gram cannot directly change the computer mode from slave
to master.
However, the slave program can gain direct
access to certain executive program operations by means
of call instructions.
The operations available through
call instructions are established by the resident execu-
tive program.
CPU FAST MEMORY
Several high-speed integrated circuit memories may be
used in the SIGMA 6 CPU.
These memories are cap-
able of delivering information to (or receiving informa-
tion from) the arithmetic and control unit simultaneously
with the operation of core memory.
These memories
are not accessible to any other unit in a SIGMA 6
system.
Computer Modes/CPU Fast Memory
9
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