"-
5-24
Functional
Description
Portable
PLUS
Computer
5.17
Configuration EPROM
The configuration EPROM (erasable/programmable read-only memory, designated
Al
U30 on the
memory PCA) can be configured as an 8K-byte device (standard) or as a 16K-byte device. A 32K-byte
device can be used,
but
only the upper 16K bytes are addressable, since PGM (pin 27)
is
connected to
VccS.
The EPROM is connected to the
I/O
address
and
data buses.
Typically, a configuration
EPROM contains the computer's unique serial number
and
information
about keyboard mapping, display fonts,
and
hardware configuration, including the amount of built-in
RAM
. The CPU uses this information to determine system operation. The configuration EPROM is
programmed differently for each language,
but
all versions use the same unprogrammed EPROM as a
replacement.
5.18
Plug-In
Ports
Plug-in drawers interface to the memory PCA via 62-pin connectors AIJI
and
AIJ2. Pins 1
and
2 of
these connectors must be shorted for the computer
to
turn on. Each plug-in drawer shorts these two
pins. While servicing the computer, you can install port jumpers
(HP part number 45711-60918) in-
stead. The two plug-in port connectors have identical pin configurations. Address, data,
and
miscellaneous control signals are brought out to these connectors. Address
and
data line buffers in the
plug-in drawers are used to reduce system bus loading.
5.19
System
Extensions
The following sections briefly describe available extensions of the computer's capabilities.
5.19.1 Memory (RAM)
Drawer
The HP 82981A Memory Drawer provides 128K bytes of additional
RAM
. One or two
~
82984;
(
Memory Cards can be installed in the memory drawer to provide 256K bytes or 384K bytes of
taraT
plug-in RAM. The memory cards are identical to the piggyback PCAs used internally for early E and F
versions of the mainframe. The memory drawer
PCA buffers the address bus, data bus, and control
bus lines from the mainframe.
It
provides two connectors
02
and
J3)
for connecting piggyback PCAs.
Logic contained on the memory drawer
PCA selects the appropriate
RAM
ICs, including those
on
the
piggyback PCAs.
yte Memory Drawer provides
1M
bytes of additional
RAM.
The memory drawer
ess bus, data bus,
and
control lines from the mainframe. Logic contained
on
the
memory drawer
PCA enables one of eight 128K-byte blocks of
RAM
according to information
on
the
address
and
data buses. Logic also selects individual
RAM
ICs within the enabled block according to
the address
on
the address bus.
5.19.2
Software
(ROM) Drawer
The HP 82982A Software Drawer provides sockets for installing
up
to I.5M bytes of ROM-based
software.
Using an alternative configuration, the software drawer can accomodate EPROMs, including
a bank of four
EPROM pairs emulating a single
ROM
pair.
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