•
•
Portable
PLUS
Computer
Functional
Description
5-25
The software drawer PCA (figures 12-9
and
12-10) buffers the address bus, data bus,
and
control bus
lines from the mainframe.
It
provides 12 sockets for installing the ROM
or
EPROM ICs. Six jumper
sockets
(XW1
through
XW6)
define
the
configuration
of
the installed ICs. Logic contained
on
the PCA
selects the appropriate ROMs or EPROMs.
5.19.3
Video
Interface
The
HP
8298SA Video Interface provides a connection for duplicating the computer display
on
an
external monitor. The video interface consists of a modified battery door for the computer that con-
nects to the motherboard PCA in the computer, a video cable that connects to the the battery-door
connector, a separate interface module that connects to the video cable,
and
a monitor cable that
connects the interface module to a monitor.
An
ac adapter provides power to the interface module. A
description of the interface
and
complete service information are contained in the HP
82985A
Video
Interface
Assembly-Level
Service
Manual
(part number 8298S-90003).
5.19.4
SNALink/3270
Software
Drawer
The
HP
S0922A
SNAUnk/3270
Software Drawer provides two capabilities for the Portable PLUS:
•
Synchronous RS-232 communication in
an
IBM
Systems Network Architecture (SNA) environment.
The computer emulates
an
IBM
3270 display station, enabling a remote connection to
an
IBM
host
computer.
Two
socketed ROM ICs provide the supporting software .
• Sockets for installing
up
to 1M bytes of ROM-based software. A jumper selects between
'ROMs'
and
'EPROMs'. The
'ROM'
configuration accomodates mixtures of 32K-byte ROM ICs, 128K-byte
ROM ICs,
and
64K-byte EPROM ICs. The 'EPROM' configuration accommodates only 32K-byte
EPROM ICs. (The SNAUnk/3270 code is provided in two ROM ICs that can be installed in two
sockets.)
The
PCA (figures 12-24
and
12-2S) buffers the address bus
(U9
and
U10)
and
data bus
(U11
and
U12)
from the mainframe. The PCA uses several
'ZHAL'
(zero-power hard-array logic) ICs to implement its
functionality.
U7 contains the control registers for the drawer's two functions. U6 contains the ID
registers.
For the serial function, serial decoder
U14 provides the control signals for the Z80 SIO controller IC
U2. The controller transfers data between the serial port
and
the data bus according to the control
signals from
U14
and
from the serial port. Voltage converters
US
and
U6 produce
the
+ lOV
and
-10V
supplies for the serial port. Oscillator
U13
provides the reference clock for the synchronous
serial port. Table S-4 lists the pin assignments for
the
serial cable used with the SNALink/3270
drawer.
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