Specifications

2.3 Power-On Self-Test
Before the applicationDEC 400xP system can be used, all components must be
initialized and tested, and the operating system must be loaded into memory.
The BIOS that is stored in ROM controls this sequence of actions. A portion
of the BIOS contains a power-on self-test (POST). POST is responsible for
initializing and testing system components each time power is applied or when
the system boots. The remainder of the BIOS loads the operating system and
specific applications.
Each time you turn on the system, POST displays a numeric countdown (880
to 000) sequence as it tests the system board, Intel 486, system board timers
and logic devices, keyboard, memory, and so on. POST countdown numbers
800 through 520 are not displayed on the monitor, but are represented as beep
codes (see Section 2.3.5).
The power-on self-tests are divided into two types of tests: system board
hardware and peripheral hardware. The following sections describe these tests
as well as the POST sequence and POST messages.
2.3.1 System Board Hardware Tests
Post checks the system board hardware first. If any of these tests fails, a fatal
error condition exists and further testing and initialization is not possible.
You are notified that an error condition exists by an error message displayed
on the monitor or by beeps from the system speaker. Refer to Section 2.3.4
for descriptions of the POST messages and Section 2.3.5 for more on the beep
codes. The following list of the system hardware tests shows the order of
execution:
CPU
ROM BIOS (checksum)
Programmable interrupt timer (PIT)
Base 64 KB DRAM
CMOS RAM
EISA devices
DMA controller
Programmable interrupt controller (PIC)
Video controller
Keyboard controller
Real-time clock
2–2 System Troubleshooting