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Jr J~) ~ Field Engineering
Theory of Operation
System/360 Model 40
Comprehensive Introduction
SY22-2840-2
Preface
This manual describes the basic data flow, machine
instruotion, and channel operations of the IBM 2040
Processing Unit. The basic numbering systems used
within the IBM System/360 are explained in detail. A
thorough understanding of this information is helpful
in the study of the more complex units of the system.
Other manuals useful in understanding the Model
40 are:
IBM System/360 Model 40, Functional Units, Order
No. SY22-2843
IBM System/360 Model 40, Theory of Operation,
Order No. SY22-2844
IBM System/360 Model 40, Power Supplies, Fea-
tures, and Appendix, Order No. SY22-2845
IBM System/360 Model 40, Maintenance Manual,
Order No. SY22-2841
IBM System/360 Model 40, Diagrams Manual, Or-
der No. SY22-2842
Solid Logic Technology Power Supplies, Order No.
SY22-2799
Solid Logic Technology, Packaging, Tools, and
Wiring Change, Order No. SY22-2BOO
This manual is written to engineering change level
254814 for ALD'S and CLD level 255263.
Sixth Edition (April, 1970)
This edition, Order No. SY22-2840-2, is a reprint of Form Y22-2840-1 incorporating
changes released in FE Supplement Y22-6783, dated January 31,1969. Changes are
periodically made to the specifications herein; any such changes will be reported in
subsequent revisions or FE Supplements.
This manual has been prepared by the IBM Systems Development Division, Product
Publications, Dept. B96, P.O. Box 390, Poughkeepsie, N.Y. 12602. A form for
readers' comments is provided at the back of this publication. If the form has been
removed, comments may be sent to the above address.
(0 Copyright International Business Machines Corporation 1966, 1970
Contents
Introduction to IBM System/360 Model 40 5 Standard Interface .............. . 36
System/360 ... . ............. . 5 Input/Output Operations 36
The Processor Family. . . . . ........ . 5 Channel Types ... . .................. . 37
Flexibility and Compatibility . . . . . . .. . ...... . 6 Channel Operation .......................... . 38
System/360 Model 40 . . . ....... . 6 Channel Program ............. . 38
Computer Functional Units ....... . 6 Device Addressing .............................. . 39
Functional Units - System/360 Model 40. 9 Channel Address Word ( CAW) . 40
Channel Command Word (CCW) 40
Data Formats . . . . . . . . . . . . . . ........ . 10 Channel Control ............. . 41
Data Coding .......... . ........ . 10 Channel Status ............... . 42
Binary Coding . . . . . . . . . .... 10 I/ 0 Instructions . . . . . . .. 43
Hexadecimal Coding . . ...... . 13 Interrupts ........ . 45
Decimal Coding .. ................... 13 Generation and Stacking of I/O Interrupts. 45
Data Codes for Input/Output. . ...... . 14 Clearing of I/O Interrupts 46
Other Data Codes 16 Sequencing Channel Interrupts .... 47
Binary Fixed-Point Arithmetic 16 I/O Interrupt Handling .... 47
Add and Subtract 16 Examples of Interrupt Sequencing. 47
Multiply ....... . 17 Initial Program Load (IPL) 49
Divide ....... . 17 ~1 ultiprogramming 49
Floating-Point Arithmetic 17 System/360 Concept 50
Exponential Numbers 18 Operating System Principles 51
Floating-Point Notation 18 Error Detection and Handling 52
Decimal Arithmetic 20 Machine .Malfunctions 52
Programming Errors 52
System Controls 22
Instructions .. 22 Basic Data Paths .......... . 53
Instruction Format 22 Main Registers and 16-Bit Data Flow ........... . 53
Address Generation 23 ALUand 8-Bit Data Flow. 53
Instruction Types ......... . 24 Staticizer Latches (Stats) 53
Data-Handling Instructions 24 Local Storage and Addressing .................. . 53
Branch Instructions 27 Main Storage (MS) 55
Sequential Instruction Execution 28 Data Transfers ......... . 56
Program Status ................... . 29 Addressing ........... . 56
Program Status 'Word (PSW). 29 Extended Addressing 56
Status Switching Instructions .. 30 Special Area 56
Interrupt System .......... . 30 Control 56
Types of Interrupts 31 Channels 57
Permanent Main Storage Locations. 31 Multiplex 57
Priority of Interrupts ....... . 32 Selector Channel 57
Masking of Interrupts in PSW. 32
Interrupt Code in PSW. . ...... . 33 Basic System Timing 59
Instruction Length Code (ILC) in PSW. 34 CPU Timing 59
CPU Status ..................... . 34 CPU and MS Timing 59
I/O System 35
Sample System Configuration 35 Microprogramming Concepts 61
List of Illustrations
FIGURE TITLE PAGE FIGURE TITLE PAGE
Introduction to IBM System/360 Model 40 15. Sample System Configuration 35
1. System Configurations 7 16. Channel Command Word Format. 40
2. Functional Parts of a Computer. 8 17. Channel Status Word Format .. 42
3. Functional Parts of IBM 2040. 8 18. Initial System Status 48
19. Situation After Steps 1 to 6. 48
Data Formats 20. Situation After Steps 7 to 10. 48
4. Data Formats 11 21. Situation After Steps 11 to 13 49
5. Powers of Two 12 22. Situation After Steps 14 to 16. 49
6. Packed Decimal Format 13
14 Basic Data Paths
7. EBCDIC and ASCII Tables
8. Extended Card Code. 15 23. 2040 Simplified Data Flow. 54
9. Zoned Decimal Format 16 24. ~lain Registers and 16-Bit Data Flow. 55
10. Floating-Point Format 19 25. ALU and 8-Bit Data Flow Added. 55
26. Staticizer Latches Added 55
System Controls 27. Local Storage Added .................. . 55
11. Five Basic Instruction Formats 22 28. Main Storage and 16-Bit Buses Added. 56
12. Alphabetic List of Instructions (Sheet 1 of 2) . 25 29. Read Only Storage Added 57
12. Alphabetic List of Instructions (Sheet 2 of 2) .. 26
13. Program Status "Vord Format. 29 Basic System Timing
14. Permanent Storage Assignments 32 30. Timing Relationships 60
Abbreviations
AO A Register byte 0 LS Local Storage
Al A Register byte 1 LSAR Local Storage Address Register
AX A Register Extension LSD Least Significent Digit
ALU Arithmetic and Logic Unit MAP Maintenance Analysis Procedure
AMWP Bits 12-15 of the PS\V MC Machine Check
A Reg A Register MDM Maintenance Diagram Manual
ASCII American Standard Code for Information MI Maskable Interrupt
Interchange MS Main Storage
B Base Register MSC Machine Status Chart
BCD Binary Coded Decimal MSD Most Significant Digit
BCDIC Binary Coded Decimal Interchange Code MSS Manual Single Shot
B Reg B Register OS Operating System
CAS Control Automation System P Parity (,bit)
CAvY Channel Address Word PC Parity Check
CC Chain Command PCI Program Control Interrupt
CC Condition Code PG Parity Generation
CCW Channel Command Word PRI Program Interrupt
COA Chain Data Address Prg Chk Program Check
CE Channel End PSA Protected Storage Address
CI Command Immediate PSW Program Status Word
CLD CAS Logic Diagram Pty Parity
CLFC Condensed Logic Flow Chart Rx Operand Register
COBOL Common Business Oriented Language ROAR Read Only Address Register
CPU Central Processing Unit ROBAR Read Only Back-up Address Register
C Reg C Register ROS Read Only Storage
CSW Channel Status Word ROSCAR ROS Channel Address Register
CT Count RR Register-to-register operations
CU Control Unit RReg R Register
CX C Register Extension RS Register-to-storage operations
CO C Register byte 0 rtpt reinterpret
Cl C Register byte 1 RX Register-to-indexed-storage operations
D Displacement Address RX R Register Extensions
DReg D Register RO R Register byte 0
DO D Register byte 0 Rl R Register byte 1
Dl D Register byte 1 R/W Read/write
DE Device End SAB Storage Address Bus
Decr Decrement SAT Storage Address Test
Del Delayed SC Selector Channel
Des Destination SI Storage-and -immediate-operand operation
DM Diagnostic Monitor SIO Start 110 (Input/Output)
EBCDIC Extended Binary Coded Decimal Interchange SILl Suppress Incorrect Length Indicator
Code SLT Solid Logic Technology
EC Engineering Change SMS Standard Modular System
ECAD Error Checking Analysis Diagram SP Storage Protect
SPLS Storage Protect Local Storage
FNB Functional Branch S Reg S Register
FORTRAN Formula Translating System SS Storage-to-storage operation
FP Floating Point SSK Set Storage Key
GP General Purpose (Registers) STATS Staticizer Latches
HEX Hexaodecimal SVC Supervisor call (op code)
HIO Halt 110 (Input/Output) SX S Register Extension
SO S Register byte 0
I Immediate Data (not in text) SI S Register byte 1
IB Instruction Buffer
IC Instruction Count TCH Test Channel
ICC Interface Control Check TIC Transfer in Channel
ID Inhibit Dump TIO Test 110 (Input/Output)
IOQ Invalid Decimal Digit (on Q bus) TROS Transformer Read Only Storage
IF Interface UBA Use Bump Address
ILC Instruction Length Code UCW Unit Control Word
110 Input/Output Unobt Unobtainable
IOCS Input/Output Control System
IPL Initial Program Load WLR Wrong Length Record
IR Interrupt Request X Index Register
ISA Invalid Storage Address YC Carry Latch
ISK Insert Storage Key YCH 1,3 Selector Channel Stats 1, 3
IZT Integrated Zero Test YCI Indirect Function Carry Stat
L Operand Length YCO Direct function Carry Stat
LDB Load Button ~P Microprogram
Introduction to IBM System/360 Model 40