IBM System/370-XA is an instruction set architecture introduced by IBM in 1983 with the IBM 308X processors. It extends the IBM System/370 architecture to support 31-bit virtual and physical addresses, and includes a redesigned I/O architecture.
Quick Facts Designer, Bits ...
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Quick Facts Bits, Field ...
IBM S/370-XA registers
General Registers 0-15
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Two's complement value |
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0 |
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31 |
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Control Registers 0-15
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See Principles of Operation[1]: 4-6–4-8 |
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0 |
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31 |
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Floating Point Registers 0-6
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S |
Biased exponent |
Mantissa |
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0 |
1 |
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7 |
8 |
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31 |
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Mantissa (continued) |
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32 |
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63 |
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Extended Architecture Extended Control mode PSW[1]: 4-5–4-6
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0 |
R |
0 |
0 |
0 |
T |
I O |
E X |
Key |
1 |
M |
W |
P |
S |
0 |
CC |
Program Mask |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
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0 |
1 |
2 |
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4 |
5 |
6 |
7 |
8 |
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11 |
12 |
13 |
14 |
15 |
16 |
17 |
18 |
19 |
20 |
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23 |
24 |
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31 |
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A |
Instruction Address |
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32 |
33 |
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S/370-XA EC mode PSW abbreviations
Bits |
Field |
Meaning |
1 |
R |
PER Mask |
5 |
T |
DAT mode |
6 |
IO |
I/O Mask; subject to channel mask in CR2 |
7 |
EX |
External Mask; subject to external subclass mask in CR0 |
8-11 |
Key |
PSW key |
12 |
E=1 |
Extended Control mode |
13 |
M |
Machine-check mask |
14 |
W |
Wait state |
15 |
P |
Problem state |
16 |
S |
Address-Space Control 0=primary-space mode 1=Secondary-space mode |
18-19 |
CC |
Condition Code |
20-23 |
PM |
Program Mask
Bit |
Meaning |
20 |
Fixed-point overflow |
21 |
Decimal overflow |
22 |
Exponent underflow |
23 |
Significance |
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32 |
A |
Addressing mode 0=24 bit; 1=31 bit |
33-63 |
IA |
Instruction Address |
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- IBM documentation numbers the bits from high order to low order; the most significant (leftmost) bit is designated as bit number 0.
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