IBM XT 5160 User Manual

Keyboard Buffer
A 16-byte first-in-first-out (FIFO) buffer in the keyboard stores
the scan codes until the system
is ready to receive them.
A buffer-overrun condition occurs when nlore than 16 bytes are
placed in the keyboard buffer.
An overrun code replaces the 17th
byte. If more keys are pressed before the system allows keyboard
output, the additional data
is lost.
When the keyboard
is allowed to send data, the bytes in the
buffer will be sent as in normal operation, and new data entered
is
detected and sent. Response codes do not occupy a buffer
position.
If keystrokes generate a multiple-byte sequence, the entire
sequence must fit into the available buffer space
or the keystroke
is discarded and a buffer-overrun condition occurs.
Keys
With the exception of the Pause key, all keys are make/break.
The make scan code of a key
is sent to the keyboard controller
when the key
is pressed. When the key is released, its break scan
code
is sent.
Additionally, except for the Pause key, all keys are typematic.
When a key
is pressed and held down, the keyboard sends the
make code for that key, delays 500 milliseconds
± 20%, and
begins sending a make code for that key at a rate of 10.9
characters per second
± 20%.
If two or more keys are held down, only the last key pressed
repeats at the typematic rate. Typematic operation stops when
the last key pressed
is released, even if other keys are still held
down. If a key
is pressed and held down while keyboard
transmission is inhibited, only the first make code
is stored in the
buffer. This prevents buffer overflow as a result of typematic
action.
4-24
lOl/102-Key Keyboard

IBM XT 5160 Specifications

General

Brand	IBM
Model	XT 5160
Category	Desktop
Language	English

Summary

Technical Reference

Federal Communications Commission Radio Frequency Interference Statement

Details FCC compliance for radio frequency interference.

Preface

Introduces the publication's scope, intended audience, and structure.

System Block Diagram (XT)

Illustrates the functional components of the IBM Personal Computer XT system unit.

System Block Diagram (Portable)

Illustrates the functional components of the IBM Portable Personal Computer system unit.

Expansion Unit Block Diagram

Illustrates the functional components of the expansion unit.

Section 1: SYSTEM BOARD

Covers the main system board components, including microprocessor, memory, and I/O.

Section 2: COPROCESSOR

Details the Intel 8087 math coprocessor and its interfaces.

Section 3: POWER SUPPLIES

Describes the power supplies for the IBM Personal Computer XT and Portable models.

Section 4: KEYBOARDS

Covers the 83-key and 101/102-key keyboards, including their descriptions, layouts, and scan codes.

Section 5: SYSTEM BIOS

Explains the Basic Input/Output System (BIOS) usage, listings, and interrupt vectors.

Section 6: INSTRUCTION SET

Details the 8088 and 8087 instruction sets, including registers and operation summaries.

Section 7: CHARACTERS, KEYSTROKES, AND COLORS

Provides information on character codes, keystroke functions, and text attributes for different adapters.

Glossary

Defines terms used in the manual.

Bibliography

Lists reference materials used in the creation of this manual.

Index

Provides an alphabetical listing of topics for quick reference.

Section 1: SYSTEM BOARD

Description

Provides an overview of the system board's physical characteristics and layout.

Microprocessor

Details the Intel 8088 microprocessor, its specifications, and operation.

Data Flow Diagrams

Presents diagrams illustrating data flow within the system board.

System Memory Map

Outlines the memory allocation for different system configurations.

System Timers

Explains the function and operation of the system's programmable timers.

System Interrupts

Describes the prioritized interrupt levels and their assignments.

System Boards

Details the different system boards (64/256K, 256/640K) and their memory configurations.

Specifications

Lists technical specifications for the system unit, including size, weight, and environment.

Card Specifications

Provides dimensional specifications for option cards.

Connectors

Details the system board's connectors, including power supply and keyboard interfaces.

Logic Diagrams - 64/256K

Presents detailed logic diagrams for the 64/256K system board.

Logic Diagrams - 256/640K

Presents detailed logic diagrams for the 256/640K system board.

Section 2: COPROCESSOR

Description

Explains the function of the 8087 math coprocessor in enhancing system performance.

Programming Interface

Details the data types, registers, and instructions extended by the coprocessor.

Hardware Interface

Describes how the coprocessor interfaces with the system bus and clock generator.

Section 3: POWER SUPPLIES

IBM Personal Computer XT Power Supply

Details the specifications, input requirements, and outputs of the XT power supply.

IBM Portable Personal Computer Power Supply

Details the specifications, input requirements, and outputs of the Portable Personal Computer power supply.

Section 4: KEYBOARDS

83-Key Keyboard Description

Describes the features and commonalities of the 83-key keyboard.

Keyboard Encoding and Usage

Explains how keyboard scan codes are converted and used by the system.

Keyboard Layouts

Illustrates the different physical layouts available for IBM keyboards.

Connector Specifications

Details the pin assignments for keyboard connectors.

101/102-Key Keyboard

Describes the features and operation of the 101/102-key keyboard.

Section 5: SYSTEM BIOS

System BIOS Usage

Explains how the BIOS provides device-level control and system services.

Vectors with Special Meanings

Details specific interrupt vectors used by the BIOS.

System BIOS Listing - 11/22/85

Provides an assembly language listing of the BIOS dated 11/22/85.

Quick Reference - 256/640K Board

Offers a quick reference for BIOS routines on 256/640K systems.

System BIOS Listing - 11/8/82

Provides an assembly language listing of the BIOS dated 11/8/82.

Quick Reference - 64/256K Board

Offers a quick reference for BIOS routines on 64/256K systems.

Section 6: INSTRUCTION SET

8088 Register Model

Details the 8088 microprocessor registers and their functions.

Memory Segmentation Model

Explains the 8088's memory segmentation architecture.

Segment Override Prefix

Describes the segment override prefix instruction.

8088 Instruction Set

Lists and describes the 8088 microprocessor's instructions.

8087 Coprocessor Instruction Set

Details the instructions supported by the 8087 math coprocessor.

Section 7: CHARACTERS, KEYSTROKES, AND COLORS

Character Codes

Provides a comprehensive table of character codes, keystrokes, and text attributes.

Quick Reference

Offers a quick reference for character codes and text attributes.

Glossary

Bibliography

Index