IBM PC CONVERTIBLE Use and care manual

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First Edition (February 1986)
THE FOLLOWING PARAGRAPH DOES NOT APPLY TO THE
UNITED KINGDOM OR ANY COUNTRY WHERE SUCH
PROVISIONS ARE INCONSISTENT WITH LOCALLAW:
International Business Machines Corporationprovides this manual "asis,"
without warranty of any kind, eitherexpress or implied, including, but not
limited to, the particularpurpose. IBM may make improvements
and
changes in the products and the programsdescribed inthis manual at any
time.
This productcouldinclude technical inaccuracies ortypographical errors.
Changes are periodically made to the informationherein; these changes will
be incorporated in new editions
of the publication.
It is possible thatthis material maycontain reference to,
or information
about, IBM products(machines
and programs), piOgramming, or services
thatare notannouncedin yourcountry. Such references or information
must not be construed to meanthatIBM intends to announce such IBM
products, programming,
or services inyourcountry.
Productsare notstocked atthe addressbelow. Requests for copies
of the
product
and for technical information aboutthe system shouldbe made to
yourauthorized IBM Personal ComputerDealer.
THE FOLLOWING PARAGRAPH APPLIES ONLY TO THE UNITED
STATES AND PUERTO RICO: Aform for reader'scommentsis
providedatthe back
of this publication. If the form hasbeen removed,
commentsmaybe addressed to IBM Corporation, Department95H, 11400
Burnet Road, Austin, Texas 78758, U.S.A. IBM may use or distribute
whateverinformation you supply in any way itbelieves appropriate without
incurring any obligation to you.
All specifications are subjectto change without notice.
©Copyright International Business Machines 1986

Preface
The IBM PCConvertible Technical Reference consists of two
volumes. Volume 1describes the hardware design
and
provides interface information for the IBM PCConvertible.
Volume 1also has information about the basic
input/output
system (BIOS) and programming support. Volume 2 contains
the BIOS listings.
The information in these volumes is both descriptive
and
reference-oriented and is intendedfor hardware and software
designers, programmers, engineers,
and otherinterested
persons who need to understand the design
and operation of
the IBM PC Convertible. These users should be familiar with
the use
of the IBM PCConvertible and understand the
concepts
of computerarchitecture and programming.
Volume 1has five sections:
• Section 1, "Introduction"is an overview of the system and
theavailable options.
• Section 2, "System Unit" describes each functional part of
thebase system. This section also contains thedescription
of the interfaces. Programmingconsiderationsare
supportedby
command code and registerdescriptions.
• Section 3, "System Options" describes each available
option.
• Section 4, "System BIOS and Usage" describes thebasic
input/output system (BIOS) and its use. This section also
containsthe software interruptlisting, a system memory
map, descriptions
of vectors with special meanings, and a
set oflow-storage maps.
In addition, Section 4 describes
keyboard encoding
and usage.
• Section 5, "Compatibilitywith the IBM Personal
ComputerFamily" describes programmingconcerns for
maintainingcompatibilityamongthe IBM PC
Convertible system
and the other IBM Personal
Computers.
iii

Volume 1has thefollowing appendixes:
• Appendix A, "Characters and Keystrokes"
• Appendix
B, "Unit Specifications"
• Appendix
C, "Logic Timing Diagrams"
• Appendix D, "Power-OnSelfTestErrorCodes".
Volume 2contains the BIOS listing and is to be used in
conjunctionwith Volume 1.
Prerequisite Publications
Guideto Operations: for the IBM PC Convertible.
Suggested Reading
• BASIC for the IBM Personal Computer
• Disk OperatingSystem
• Hardware Maintenance
and Servicefor the IBM PC
Convertible
• MACRO Assemblerfor the IBM Personal Computer.
iv

Contents
Section 1. Power-On Self-Test (POST) ............... 1-1
Power-On Self-Test Sequence .................. 1-2
Modem Presence Test ........................ 1-9
Printer/CommunicationsPresence Test ......... 1-12
Section 2.
ROM BIOS Listing ...................... 2-1
ROMMap ................................. 2-4
Common Equates and Data Areas ............... 2-7
Nonmaskable Interrupt Handler(BlONMIH)
.... 2-26
Keyboard Services
(BIIKYBD) ............... 2-65
Video I/O and Print Screen (BI2VIDEO) ........ 2-77
Diskette Support
(B 13DSKT) ................ 2-119
Communications
and PrinterBIOS
(B14COMMO)
........................... 2-143
Time
of Day(B15TOD) ..................... 2-153
System Services
(B 16SYSV) . . . . . . . . . . . . . . . . . . 2-168
General Subroutines
and Tables (B 17TABLE) ... 2-191
Release Date Marker ....................... 2-241
System Model Byte
......................... 2-241
v

Notes:
vi

Section 1. Power-On Self-Test
(POST)
The IBM PC Convertibleuses a set of routines called the
power-on self-test(POST) routines. These routines
automaticallyactivate system power, perform basic function
and device controltestsfor the majorsystem components,
and initializethesystem to theready state. Because the
operation
of these routines is automatic and cannotbe
changed by anapplication programmer, theactual program
listingsare not included
in this manual. However, it may be
useful to understandthefunction
of these routines and the
initial values they
may establish.
Figure
I-Ion page 1-2 shows the sequence of thesteps the
power-on routines, theerrorindicatorsreturned,
and the
initial values established. Figure
1-2 on page 1-9 and Figure
1-3 on page 1-12 provide additional information on testingfor
thepresence
of devices.
Power-OnSelf-Test (POST) 1-1

Power-On Self-Test Sequence
Description ErrorIndication
Processortest: Verifies processor System power off.
operation.
System ROM checksum test: I-long
and I-short
Verifies system ROM. beep, then system
power off.
Real-iimeclock RAM test: Verifies l-iong
and I-short
the clock.
If contents havebeen beep, then system
altered, RAM is cleared
and poweroff.
system profile defaults are loaded.
Power source and batterycheck: 3-shortbeeps, then
Checks for external power.
If no system poweroff.
external power, checks for good
battery.
Base 8K RAM test: Validates first I-long and I-short
8K of RAM and clears it to zero. beep, thensystem
poweroff.
Internal modem poweron: Checks
for internal
modem presence and
applies powerto itifpresent. See
Figure
1-2 on page 1-9 for
additionalinformation.
Figure 1-1 (Part 1of7). Power-on Self-TestSequence
1-2 Power-OnSelf-Test (POST)

Description
Error Indication
Video adapterpresencetest:
Checks for attached video
adaptersby nondestructive writing
and readinghex A55A to address
hex
BOOOO and B8000. Checks for
videoadapterswith valid rom.
Checks for
LCD bydetermining if
the 'LCD sense' line is set.
Video interrupt vectors
initialization:Initializeshex
10,
ID, IF and 44 video interrupt
vectors to system defaultvalues.
Video ROM validitytests: Checks
for videoadapterwith valid ROM.
See Volume I for additional
information
about adapterswith
system accessible ROM. Links to
ROM if valid.
LCD function test: Runs LCD
Error 5001, 5002, or
function test if the LCDis present. 5003
CRT adapter without ROM Error 0501
presenceandfunction tests: Ifa
CRT adapterwithout ROM is
present, test vertical
and
horizontal syncs.
Operabledisplaypresencetest: I-long and 2-short
Checks to ensure
that an operable beeps, then system
display is present. poweroff.
Figure1-1 (Part 2 of 7). Power-onSelf-TestSequence
Power-On Self-Test (POST) 1-3