HelpPC 2.10 Quick Reference Utility Copyright 1991 David Jurgens

               POST - Cold Boot / Power On Self Test Activities

       - power supply starts Clock Generator (8284) with Power
         Good signal on BUS
       - CPU reset line is pulsed resetting CPU
       - DS, ES, and SS are cleared to zero

       Cold and Warm Boot both execute the following sequence
       - CS:IP are set to FFFF:0000 (address of ROM POST code)
       - jump to CS:IP  (execute POST, Power On Self test)
       - interrupts are disabled
       - CPU flags are set, read/write/read test of CPU registers
       - checksum test of ROM BIOS
       - Initialize DMA (verify/init 8237 timer, begin DMA RAM refresh)
       - save reset flag then read/write test the first 32K of memory
       - Initialize the Programmable Interrupt Controller (8259)
         and set 8 major BIOS interrupt vectors (interrupts 10h-17h)
       - determine and set configuration information
       - initialize/test CRT controller & test video memory (unless 1234h
         found in reset word)
       - test 8259 Programmable Interrupt Controller
       - test Programmable Interrupt Timer (8253)
       - reset/enable keyboard, verify scan code (AAh), clear keyboard,
         check for stuck keys, setup interrupt vector lookup table
       - hardware interrupt vectors are set
       - test for expansion box, test additional RAM
       - read/write memory above 32K (unless 1234h found in reset word)
       - addresses C800:0 through F400:0 are scanned in 2Kb blocks in
         search of valid ROM.  If found, a far call to byte 3 of the ROM
         is executed.
       - test ROM cassette BASIC (checksum test)
       - test for installed diskette drives & FDC recalibration & seek
       - test printer and RS-232 ports.  store printer port addresses
         at 400h and RS-232 port addresses at 408h.  store printer
         time-out values at 478h and Serial time-out values at 47Ch.
       - NMI interrupts are enabled
       - perform INT 19 (bootstrap loader), pass control to boot record
         or cassette BASIC if no bootable disk found
       - WARM BOOT procedure is now executed

       - see   DIAGNOSTIC CODES

Esc or Alt-X to exit cold boot Home/PgUp/PgDn/End ←↑↓→
Converted to HTML in 2006 by Timo Bingmann