Specifications

CHAPTER 1
INTRODUCTION
This publication is a handbook for Digital Equipment Corporation’s PDP-11.
It provides a comprehensive overview of the system structure, the instruction
repertoire, input/output programming, peripherals, general interfacing, soft-
ware, and console operation.
PDP-11 is Digital’s answer to the demand for a modular system for real-time
data acquisition, analysis and control. PDP-11 systems can handle a wide
variety of real-time control applications-each system being individually
tailored from a comprehensive array of modular building blocks. Digital is
unique among manufacturers of small-scale computers-in its ability to pro-
vide not only fast and efficient processing units, but also a large family of its
own compatible I/O devices including A/D and D/A converters, magnetic
tape, disk storage, paper tape, and displays, as well as a wide range of
general-purpose modules. This capability offers the user a hew, more efficient
approach to real-time systems.
The following paragraphs introduce the new PDP-11 by way of highlighting
several of the important design features that set it apart from other machines
in its class. Subsequent chapters of this manual place these features in their
proper context and provide detailed descriptions of each.
PDP-11 SYSTEMS
The PDP-11 is available in two versions designated as PDP-ll/ 10 and PDP-
11/20. The PDP-ll/ 10 contains a KAll processor, 1,024 words of 16-bit
read-only memory, and 128 16-bit words of read-write memory. The basic
PDP-ll/PO contains a KAll processor and 4,096 words of 16.bit read-write
core memory, a programmer’s console, and an ASR-33 Teletype. Both ver-
sions can be similarly expanded with either read-write or read-only memory
and peripheral devices.
UNIBUS _
Unibus is the name given to the single bus structure of the PDP-11. The
processor, memory and all peripheral devices share the same high-speed
bus. The Unibus enables the processor to view peripheral devices-as active
memory locations which perform special functions. Peripherals can thus be
addressed as memory. In other words, memory reference insfructions can
operate directly on’control, status, or data registers in peripheral devices.
Data transfers from input to output devices can bypass the processor com-
pletely.
KAll PROCESSOR
The KAll processor incorporates a unique combination of powerful features
not previously available in ldbit computers.
Priority Interrupts-A four-level automatic priority interrupt system permits
the processor to respond automatically to conditions outside the system, or
in the processor itself. Any number of separate devices can be attached to
each level.
Each perkpheral device in a PDP-11 system has a hardware pointer to its own
unique pair of memory locations which, in turn, point to the device’s service
routine. This unique identification eliminates the need for polling of devices
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