Electrocution - Publishers of The BIOS Companion

"The computer book of the month is The Bios Companion by Phil Croucher. Long-time readers of this column will recall I have recommended his book before. This tells you everything you ought to know about the BIOS in your system. Post codes, options, upgrades, you name it.

Years ago, I called an earlier edition of this invaluable and I see no reason to change my view. Recommended."

Jerry Pournelle
Byte Magazine

"Croucher's book was invaluable 20 years ago and remains so today...... Every one of the 468 pages holds useful information, the author having zero tolerance for padding."

Davey Winder
PC Plus Magazine

"You've completerly impressed me with the quality and scope of your guides - extreme care has obviously gone into their research and preparation."

Jeremy Fleming

"His style is lovely: clear, jargon-free where possible, chatty and friendly with beautiful short paragraphs. It [Communications & Networks] joins my list of 'I wish I'd written it' books. I haven't come across such a good subject book in a long time at this price."

Lorna Kyle
Personal Computer World

"To any micro owner who wants to know what this comms business is all about, [Communications & Networks] is certainly one of the best around. ... Croucher is not only knowledgable about his subject, he's interested in it and communicates that interest to you. "

Ron Peck
New Computer Express

"There are few books about which explain as accurately and comprehensively as [Communications & Networks] does what communications are all about. The glossary is excellent."

Micro Decision

"...any PC user with a genuine interest in using his machine to its full potential will recognise [Communications & Networks] for the completely invaluable tool and often the inspiration that it is."

Yvonne Taylor
Which PC

"[Communications & Networks] is the type of book you can read on a bus or train without getting a headache from trying to understand what it means."

Network

"As a recently reformed computer illiterate myself, I appreciated the author's straighforward yet humourous and light-hearted style of writing. He manages to strike the balance between too much and too little information. ... [Computing Under Protest] is never in danger of either boring or confusing the reader."

Emma Tyrrall
Practical PC

"Good documentation is important for any software, but even more so for an operating system - the documentation [for DOS 386 Professional] has some exceptionally clear explanations. Altogether, the documentation is an example of the right way of doing things, and other software manufacturers would do well to take note."

Matthew Holbrook
Computer Shopper

"The DOS 386 Professional manual sets arrived at 2130 local time today. We have had a brief look at them and wish to congratulate IMS on the excellent, clear and concise manner in which they have been presented."

Fred Parker
ETL Soft

"I remain impressed by Mr. Croucher's fluid writing style, practical orientation, enthusiasm, and strong technical knowledge."

Lance A Leventhal
Slawson Communications, Inc

JAR Professional Pilot Studies

"Its real value lies in taking the plethora of booklets and ring-bound photocopies associated with commercial examinations and condensing them into an attractive and portable form. The guy really does deserve a medal ~ he has made a genuine contribution to the body of professional aviation literature assembled during the course of the last century.

I heartily recommend it to students of commercial flight, if only as a souvenir of their efforts... "

Colin Hilton
Pro Pilot's Rumour Network

"(The) Book is quite a good compliment to our notes for students. We will be recommending all our students buy the books.... "

Chris
Naples Air Centre

"I got your book last month and am in the process of ploughing through it! Actually, I really like it and find it very interesting and easy to read."

Simon Rouse

"So far I have found your book an extremely helpful reference manual to carry around in my flight bag."

Blair Clubley

"I wish to commend you on a "work of art". I wish the CAA would produce a quick reference easy to read manual such as yours. Truly wonderful!"

Ebrahim Parkar

Post Codes
Acer ALR AMI Arche AST AT&T	Award Chips & Technologies Compaq Dell DTK Eurosoft/Mylex	Faraday A-Tease HP IBM Intel Landmark Microid/MR NCR	Olivetti Philips Phoenix Quadtel Supersoft Tandon Zenith

Olivetti POST Codes

For EISA and PS/2, the code is issued after the test has passed, so a stuck code indicates the next test failed. Codes are sent to printer ports 3BC (the mono adapter's parallel port), 278, or 378; they will not be printed because no strobe data is sent. AT&Ts using the Olivetti motherboard and BIOS (e.g. the AT&T 6300) do the same.

Note: Not all POST codes are included below - the latest information is in the The BIOS Companion, which contains over 100 pages of them.

1076/AT&T 6312
M20
M21 & M24/AT&T 6300
PS/2

1076/AT&T 6312 Codes

The first checkpoint, 40, resets and initializes a test monitoring device on the parallel port. When an error occurs, the most recent checkpoint code sent to port 378 is exclusive-ored with 3F to complement the lower 6 bits, and then sent to 378, so if the refresh test fails (45), the POST card will show 7B because the most recent code sent before the failure was 44.

If an error occurs, the POST tries to run through activities that display a message on the monitor, showing tttt Error: xx, where tttt is the name of the failing routine, and xx is a suberror number. If the error is fatal, the display will show Unrecoverable power-up error, wait for you to press F1, and return to the failing test. If video has failed, the POST will output beep codes.

PASS FAIL DESCRIPTION

41 7F CPU flag and register test

42 7E Check and verify CMOS shutdown code

43 7D BIOS ROM checksum test

44 7C Test the 8253 timer

45 7B Start memory refresh

46 7A Test the 8041 keyboard controller

47 79 Test the first 8KB of RAM

48 78 Test protected mode operation

49 77 Test CMOS RAM shutdown byte

4A 76 Test protected mod operation

4B 75 Test RAM from 8KB to 640KB

4C 74 Test all RAM above 1MB

4D 73 Test NMI

4E 72 Test RAM parity system

50 71 Test 8259 PIC 1

51 6F test 8259 PIC 2

52 6E Test DMA page register

53 6D Test 8237 DMA controller 1

54 6C Test 8237 DMA controller 2

55 6B Test PIO port 61h

56 6A Test the keyboard controller

57 69 Test the CMOS clock/calendar IC

59 68 Test the CPU protected mode

5A 66 Test CMOS RAM battery

5B 65 Test CMOS RAM

5C 64 Verify CMOS RAM checksum

5D 63 Test parallel port configuration

5E 62 Test serial port configuration

5F 61 Test memory configuration below 640KB

60 60 Test memory configuration above 1MB

61 5F Detect and test math coprocessor

62 5E Test configuration of game port adapter

62 5D Test key lock switch

63 5D Test hard drive configuration

64 5C Configure floppy drives

66 5B Test option ROM's

- - Call interrupt 19 boot loader

M20 Codes

Not a true IBM clone, as it had a Zilog Z8001 CPU. Also, a typical POST card will not fit in a slot, so you can only monitor codes from the parallel port. The POST shows a triangle, diamond, or 4 lines on the screen to indicate early POST failure, as shown in the table.

Triangle Test CPU registers and instructions

Triangle Test system RAM

4 vertical lines Test CPU call and trap instructions

Diamond Initialize screen and printer drivers

EC0 8255 parallel interface IC test failed

EC1 6845 CRT controller IC test failed

EC2 1797 floppy disk controller chip failed

EC3 8253 timer IC failed

EC4 8251 keyboard interface failed

EC5 8251 keyboard test failed

EC6 8259 PIC IC test failed

EK0 Keyboard did not respond

Ek1 Keyboard responds, but self test failed

ED1 Disk drive 1 test failed

ED0 Disk drive 0 test failed

E10 Non-vectored interrupt error

E11 Vectored interrupt error

M21 & M24/AT&T 6300 Codes

The M24 went to the US as the AT&T 6300. It had an 8086, so was faster than the PC, albeit difficult to work on. codes are sent to 378 (LPT1). If a fatal error occurs, it performs more initialization of DMA and interrupt controller circuits, tries to display an error message, complements the lower 6 bits of the POST code, sends the result to port 378, and halts the CPU, so numbers will flicker on the POST display with bit 6 on and the lower bits running from 0 upward. The codes start at 40 because a black box was used to monitor POST status at the parallel port. Bit 6 was set true (1) to alert the box the POST was starting.

40 CPU flags and register test failed

41 BIOS ROM checksum test failed

42 Disable 8253 timer channel 1

43 8237 DMA controller test failed

44 8259 PIC test failed

45 Install the real interrupt vectors

48 Send beep and initialize all basic hardware

PS/2 Codes

01	Test CPU
02	Check CMOS shutdown byte
03	Initialize the PIC
04	Test refresh
05	Test CMOS/RTC periodic interrupt
06	Test timer ratio
07	Test first 64KB of RAM
08	Test 8042 keyboard controller
09	Test NMI
0A	Test 8254 PIT
0B	Test port 94h
0C	Test port 103h
0D	Test port 102h
0E	Test port 96h
0F	Test port 107h
10	Blank the display
11	Check the keyboard
12	Test CMOS RAM battery
13	Verify CMOS RAM checksum
14	Verify extended CMOS RAM checksum
15	Initialize system board and adapter
16	Initialize and test RAM
17	Test protected mode registers
18	Test CMOS RAM shutdown byte
19	Test CMOS protected mode
1A	Initialize video adapter ROM scan
1B	Test BIOS ROM checksum
1C	Test PIC #1
1D	Test PIC #2
1E	Initialize interrupt vectors
1F	Test CMOS RAM
20	Test extended CMOS RAM
21	Test CMOS real-time clock
22	Test clock calendar
23	Dummy checkpoint
24	Test watchdog timer
25	Test 64KB to 640KB RAM
26	Configure lower 640KB RAM
27	Test extended memory
28	Initialize extended BIOS data segment and log POST error
29	Configure memory above 1MB
2A	Dummy checkpoint
2B	Test RAM parity
2C	Test DMA page registers
2D	Test DMA controller registers
2E	Test DMA transfer-count register
2F	Initialize DMA controller
30	Test PIO 61
31	Test the keyboard
32	Initialize keyboard typematic rate and delay
33	Test auxiliary device
34	Test advanced protected mode
35	Configure parallel ports
36	Configure 8250 serial ports
37	Test and configure math co-processor
38	Test and configure game-port adapter
39	Configure and initialize hard disk
3A	Floppy-disk configuration
3B	Initialize ROM drivers
3C	Display total memory and hard drives
3D	Final initialization
3E	Detect and initialize parallel ports
3F	Initialize hard drive and controller
40	Initialize math co-processor
42	Initialize adapter ROM scan
CC	Unexpected processor excerption occurred
DD	Save DDNIL status
EE	NMI handler shutdown
FF	Call interrupt 19 boot loader