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
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0
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31
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Floating-Point Registers 0–6
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S
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Biased exponent
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Mantissa
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0
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1
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7
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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
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0
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R
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0
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0
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0
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T
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I
O
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E
X
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Key
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1
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M
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W
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P
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S
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0
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CC
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Program
Mask
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0
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0
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0
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0
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0
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0
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0
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0
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0
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1
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2
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4
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5
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6
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7
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8
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11
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12
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13
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14
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15
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16
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17
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18
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19
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20
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23
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24
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31
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A
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Instruction Address
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32
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33
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63
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S/370-XA EC mode PSW abbreviations
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Field
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Meaning
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| 1
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R
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PER Mask
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| 5
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T
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DAT mode
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| 6
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IO
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I/O Mask; subject to channel mask in CR2
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| 7
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EX
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External Mask; subject to external subclass mask in CR0
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| 8–11
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Key
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PSW key
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| 12
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E=1
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Extended Control mode
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| 13
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M
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Machine-check mask
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| 14
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W
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Wait state
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| 15
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P
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Problem state
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| 16
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S
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Address-Space Control
0=primary-space mode
1=Secondary-space mode
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| 18–19
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CC
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Condition Code
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| 20–23
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PM
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Program Mask
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Meaning
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| 20
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Fixed-point overflow
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| 21
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Decimal overflow
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| 22
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Exponent underflow
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| 23
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Significance
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| 32
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A
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Addressing mode
0=24-bit; 1=31-bit
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| 33–63
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IA
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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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IBM System/370-XA is an instruction set architecture announced by IBM on October 21, 1981 for the IBM 308X processors and available in April 1983. It extends the IBM System/370 architecture to support 31-bit virtual and physical addresses, and includes a redesigned I/O architecture.