HP Integral Personal Computer Service Manual page 23

The
logic A PCA
contains the computing electronics of the Int~ PC, including the CPU (central
processing unit), RAM (random-access memory), and MMU (memory-management unit). The key-
board controller and external
I/O
(input/output) logic circuitry are also located on the logic
A
PCA.
The internal ROM (read-only memory) is contained in the
plug-in ROM assembly,
which plugs directly
into the ROM receptacle on the logic A PCA.
The plug-in ROM assembly has room for
two
ROM PCAs: The
operating system ROM PeA
has four
ROM Ies containing the HP-UX System V operating system. The
option ROM PCA,
if present, contains
optional ROM-based software.
Note:
H
the computer is equipped with the earlier
System m
operating system, the plug-in
ROM assembly has two PCAs containing the operating system. No optional ROM can be
added to this assembly. The assembly cannot
be
serviced to the component level. It can only
be exchanged.
The
logic B PCA
contains the control circuitry
for the display, printer, disc drive, and speaker. The
speaker itseH, the RTC (real-time clock), and the HP-IB (IEEE-488) interface are also located on the
logic B PCA.
The
I/O backplane PCA
provides two I/O connectors (one each for I/O ports A and 8) and contains
no logic circuitry. .
The
display assembly
consists of an electroluminescent display panel, a display PCA, and the necessary
mounting hardware. The display assembly is a
tuned circuit.
It cannot be serviced in the field. If the
display assembly is bad, replace it.
The
power supply
provides voltages to the circuits of the computer as shown in table 5-1.
1"l1li ••
5-1.
Volta,.
Requlre ... nts
A ...... bly
+IV +12V -t2V +1SV +18V
Logic A PCA X
X X
Logic B PCA X X
Disc
Drive
X
X
Display
X X
Printer Mechanism
X
Keyboard
X
External I/O Bus
X X X
Fan
X
The rest of this chapter describes the individual components of the Integral PC.