Local Storage Registers (Lsr) - IBM System/32 Introduction And Maintenance Manual

1.8.9 Local Storage Registers (LSR)
The LSR stack contains 64 LSRs; the first 32 are
used by the base system and the remaining 32 are
reserved for optional features. Each LSR contains
16 bits, bits 0-7 are the high LSR and bits 8-15 are
the low LSR. The LSRs are called work registers
(WR) and are used as data buffers and address reg-
isters for both main and control storage. In addi-
tion, the LSRs are used as operand registers for
calculations and as I/O control data registers that
can be loaded from or sent to the I/O attachments.
The first 32 LSRs are subdivided into four groups
as shown in the LSR stack. The group of LSRs
being used depends on the current micro interrupt
level. The first group (hex address 00-07) is used
by micro interrupt level 0 (machine check interrupt)
and also by main program level.
The second group of LSRs (hex address 08-0F)
contains the MAR/MAB (microprogram address
register/microprogram address backup). MAR con-
tains the address of the next micro instruction to
be executed. MAB contains the return address
when a branch and link instruction is executed.
The third group (hex address 10-17) is used by
micro interrupt level 1 (disk), and the fourth group
(hex address 18-1 F) is used by micro interrupt
level 2 (printer, keyboard, and BSCA/SDLC).
Optional features use 10 of the remaining 32 LSRs.
The first group (hex address 20-27) is used by
micro interrupt level 3 as work registers. The
second group (hex address 28-2F) contains the
MAR/MAB for micro interrupt level 3 (hex address
28-29).
LSR Stack
Main
Level
Level a
Level 1
Level 2
Level 3
,.....
I....-
-
Micro Interrupt
a
~achine
Check)
Also used by
'Main Program Level
.----
Micro Interrupt
1
L -
(Disk)
.----
Micro Interrupt
2
(Keyboard, Printer,
and BSCA/SOLC)
Micro Interrupt
3
(Optional Features)
I
L
r-
L
I
L-
I
L
Hex
Register Address
Work Registers
WRO 00
WRl 01
WR2 02
WR3 03
WR4
04
WR5 05
WR6 06
WR7 07
Address Registers
MAR (ML) 08
MAS (ML) 09
MAR (0)
OA
MAS (0)
as
MAR (1) OC
MAS (1) aD
MAR (2)
OE
MAS (2) OF
Work Registers
WRO 10
WRl
11
WR2 12
WR3 13
WR4
14
WR5 15
WR6 16
WR7 17
Work Registers
WRO 18
WRl 19
WR2 lA
WR3 lS
WR4 lC
WR5 10
WR6 lE
WR7 lF
Work Registers
WRO
20
WRl
21
WR2
22
WR3
23
WR4
24
WR5 25
WR6
26
WR7 27
Address Registers
Used by the
base system
Used by optional
features
Introduction 1-9