Specifications

CHAPTER 5

ADDRESS ALLOCATION

The

PDP-11

provides for a very flexible addressing structure. Both 16-bit

words and 8-bit bytes can be directly addressed. Addresses are 1Bbits long

allowing for direct addressing of 32,768 words or 65,536 bytes.

ADDRESS MAP

As a result of the organization of the

PDP-11,

bus addresses serve several

functions. A map of possible PDP-11 bus address allocation is shown

BUS ADDRESS

CONTENT

Program Counter

Processor Status Word

Processor.

Trap Vectors

and Device

Interrupt

Vectors

4608

Stack Pointer Overflow Limit

Stacks, Program and Data Storage

160bOOs

Status Register and

Data Buffer Register

Device Address Register

Word Count Register

Memory Address Register

Control and Status Registers

Typical

Registers for

Programmed

Transfer

Device

Typical

Registers

for a

Block

Transfer

* Device

1777778

Figure 5-1

Simplified Address Allocation Map