HP 330 Service Information Manual page 149

Self-Test
When the machine first powers up, the boot ROM gets control. Before transferring control to
a system by booting it, the boot ROM has several responsibilities.
Hardware Initialization Support.
Some hardware must be initialized as soon as possible after power-up to prevent improper
operation. Examples are display initialization and floating RAM positioning, neither of which
can wait for an OS to be loaded.
Assembly Self-Test Support.
Self-Tests have about 95% confidence that a tested logic assembly is functioning properly. The
reason for these tests is to tell the user that the computer is working properly. This consists of
indicating all installed accessories in the computer (and expander, if connected) and reporting
all detected failures.
Boot ROM self-test routines may not identify and indicate all hardware failures correctly. Sev-
eral things contribute to this. They include hardware design and the fact that testing for 100%
of all failure types is virtually impossible.
Tests Performed by the Boot ROM
Set-Up Code Segment
A series of tests and initialization routines which set up the computer so the rest of the Boot
RO M code can function safely are the first section of Boot ROM code.
The first part of the unextendable code segment includes the following routines (note that,
before eaeh step, the LEDs are set to a new value which reflects that step):
1. Bus Error Handler:
The BUS ERROR veetor is set up to point to a routine which decides if the CPU stack
registers are functional.
2. CPU Test:
Three different values are passed, one at a time, through each of the CPU Registers. If
an error oecurs, the Boot ROM halts with a "CPU Failed" code on the LEDs.
3. Position Floating RAM and Pre-load the Top of Memory:
The Boot ROM steps through the first 16K bytes of memory, until a bus error occurs
and to initialize for the top memory test. If a bus error does not occur, the Boot ROM
starts at the top of memory and reads every 64 Kbyte boundary until a bus error occurs
or until just before the bottom RAM address is reached.
4. Cycle LEDs:
The LEDs are rippled fronl all on to all off except one. There is a snlall delay for each
ripple state which is used to cause a short delay between memory pre-load and the test
to check for memory refresh failures.
Boot ROM Functions 133